Optical pickup apparatus, recording/reproducing apparatus provided with the optical pickup apparatus, optical element and information recording/reproducing method

ABSTRACT

An optical pickup apparatus for reproducing information from an optical information recording medium or for recording information onto an optical information recording medium, is provided with a first light source for emitting first light flux having a first wavelength; a second light source for emitting second light flux having a second wavelength, the first wavelength being different from the second wavelength; a converging optical system having an optical axis and a diffractive portion, and a photo detector; wherein in case that the first light flux passes through the diffractive portion to generate at least one diffracted ray, an amount of n-th ordered diffracted ray of the first light flux is greater than that of any other ordered diffracted ray of the first light flux, and in case that the second light flux passes through the diffractive portion to generate at least one diffracted ray, an amount of n-th ordered diffracted ray of the second light flux is greater than that of any other ordered diffracted ray of the second light flux, where n stands for an integer other than zero.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to an optical pickup apparatus, arecording/reproducing apparatus with the optical pickup apparatus, anoptical element, and an information recording/reproducing method.

[0002] Recently, as the practical application of the short wavelengthred laser, a DVD which is a high density optical information recordingmedium (called also optical disk) having almost the same dimension as aCD (compact disk) and the larger capacity, comes into the production. Ina DVD recording/reproducing apparatus, the numerical aperture NA on theoptical disk side of an objective lens when a semiconductor laser of 650nm is used, is 0.6-0.65. The DVD has a track pitch of 0.74 μm, and theminimum pit length of 0.4 μm, and is in densification, in whichdimensions are lower than a half as compared to the CD having the trackpitch of 1.6 μm and the minimum pit length of 0.83 μm. Further, in theDVD, in ordered to suppress the coma which is generated when the opticaldisk is inclined to the optical axis, to be small, the transparentsubstrate thickness is 0.6 mm, which is the half of the transparentsubstrate thickness of the CD.

[0003] Further, other than the above-described CD or DVD, variousstandard optical disks in which the light source wavelength or thetransparent substrate thickness is different, for example, CD-R, RW(post script type compact disk), VD (video disk), MD (mini-disk), MO(photo-electro-magnetic disk), etc., come in the market and are spread.Further, the wavelength of the semiconductor laser is further shortened,and the short wavelength blue laser having the emission wavelength ofabout 400 nm is being into practical use. When the wavelength isshortened, even if the same numerical aperture as that of the DVD isused, the capacity of the optical information recording medium can befurther increased.

[0004] Further, in the same dimension as the CD which is theabove-described conventional optical information recording medium, thedevelopment of a plurality of optical information recording media, suchas the CD-R in which recording and reproducing can be carried out, orthe DVD whose recording density is increased, in which the transparentsubstrate thickness of the recording surface, or the wavelength of thelaser light for recording and reproducing is different, is advanced,therefore, it is required that the recording and reproducing by the sameoptical pickup can be conducted to these optical information recordingmedium. Accordingly, various optical pickups which have a plurality oflaser light sources corresponding to the using wavelength, and by whichthe laser light is converged onto the recording surface by the sameobjective lens by the necessary numerical aperture, are proposed (forexample, Japanese Tokkaihei No. 8-55363, Japanese Tokkaihei No.10-92010, etc.).

[0005] In the above description, in Japanese Tokkaihei No. 9-54973, anoptical system using a hologram optical element in which 635 nm is usedfor the transmitted light (zero ordered diffracted ray) and 785 nm isused for −first ordered diffracted ray, and an optical system using ahologram optical system in which 635 nm is used for +first ordereddiffracted ray and 785 nm is used for the transmitted light (zeroordered-diffracted ray), are disclosed. Further, in Japanese TokkaiheiNo. 10-283668, an optical system in which, the wavelength is 650 nm, ahologram ring lens is transmitted at 100%, and when 780 nm, the light isfirst ordered diffracted by the hologram ring lens, is disclosed.

[0006] However, in these hologram element and hologram-shaped ring lens,when diffraction efficiency of zero ordered light is made to be 100% forthe wavelength on one side, there surely is a limitation for diffractionefficiency of +first ordered diffracted ray or of −first ordereddiffracted ray for the wavelength on the other side, and thereby,desirable high diffraction efficiency can not be obtained, a loss of aquantity of light is caused, and efficiency of using a quantity of lightis worsened, which has been a problem. When a loss of a quantity oflight is caused, a laser of higher power is required, especially inrecording of information.

[0007] Further, in the hologram element and the hologram-shaped ringlens, when diffraction efficiency of zero ordered light is made to be100% for the wavelength on one side, and when diffraction efficiency of+first ordered diffracted ray or of −first ordered diffracted ray ismade to be great by prohibiting zero ordered light from beingtransmitted as far as possible, for the wavelength on the other side,the hologram has been made to be as deep as 3.8-5.18 μm. Therefore, whena function of a hologram optical element or of a hologram-shaped ringlens is integrated in an objective lens in particular, it is verydifficult to process a metal mold and to mold, which has been a problem.

[0008] Further, the present inventors previously proposed an objectivelens (Japanese Tokuganhei No. 9-286954) which can structure a opticalpickup which is composed of a plurality of divided surface which aredivided into concentric circular-like ones, and in which each dividedsurface is aberration corrected to the diffraction limit to a pluralityof light sources having different wavelength, and/or to the transparentsubstrate having the different thickness of the recording surface, andthe structure is simplified. This objective lens has a function by whicha necessary aperture can be automatically obtained corresponding to theusing wavelength and/or the thickness of the transparent substrate.However, when a laser/detector integrated unit in which the laser lightsource and light detector are integrated, is used, there is a problemthat a case occurs that the detection can not be correctly conducted dueto a flare light entering into the light detector. This is conspicuousparticularly in the laser/detector integrated unit of a type by whichthe light flux is deflected and introduced into the light detector byusing the hologram. Further, when high speed recording is carried out inrecordable disks in the DVD system (DVD-RAM, DVD-R, DVD-RW, DVD+R, etc.)or recordable disks in the CD system (CD-R, CD-RW, etc.), because apartial light beam becomes flare, the efficiency of use of the lightamount is bad as compared to the optical system using the exclusive uselens, therefore, it is necessary to increase the power of laser lightsource.

[0009] To both the DVD and CD whose using wavelength and transparentsubstrate thickness are different from each other, variousinterchangeable optical systems, in which one objective lens is used forrecording and/or reproducing the information without generating largespherical aberration or chromatic aberration, are proposed. However, theoptical systems which are in practical use, are structured such that thedivergence degree of the divergent light flux from the light source isweakened by a coupling lens, or the divergent light flux is made to theparallel light flux or the weak convergent light flux, and the lightflux is converged onto the information recording surface through theobjective lens and the transparent substrate of the optical informationrecording medium, and accordingly, 2 lenses of the coupling lens and theobjective lens are necessary. Accordingly, it is difficult that the sizeof the optical pickup apparatus is reduced to be small and thin, andthere is a problem that the cost is increased.

[0010] On the one hand, as described above, various optical disks exceptthe CD and DVD are spread, and therefore, an optical system which isinterchangeable to these optical disks, and whose structure is simple,and the optical pickup apparatus provided with the optical system arenecessary.

SUMMARY OF THE INVENTION

[0011] An object of the invention is to provide a pickup apparatus, arecording and reproducing apparatus, an optical element and a recordingand reproducing method, wherein one pickup apparatus can conductrecording and/or reproducing of different types of optical informationrecording media employing rays of light with at least two differentwavelengths.

[0012] Further object is to make information recording and/orinformation reproducing to be conducted by one pickup apparatus, foreach different optical information recording medium without generatingserious spherical aberration and chromatic aberration even in the caseof using rays of light having at least two different wavelengths andapplying to different types of optical information recording media. Inaddition to that, another object is to provide an optical pickupapparatus having s simple structure. In particular, when using differenttypes of optical information recording media each having a transparentsubstrate with a different thickness, the problem of sphericalaberration becomes more serious. Further object is that one pickupapparatus can conduct recording and/or reproducing of information fordifferent types of optical information recording media withoutgenerating serious spherical aberration and chromatic aberration, evenin the aforesaid occasion.

[0013] In addition, still further object is that detection of light byan photo detector can be conducted satisfactorily and sigmoidcharacteristics in detection are made to be satisfactory, withoutirradiation of flare light which affects the detection adversely on anphoto detector, even in the case of a pickup apparatus employing anintegrated unit composed of plural lasers and plural detectors.Furthermore, providing an optical pickup apparatus wherein a loss of aquantity of light is less and efficiency of using a quantity of light isexcellent, a recording and reproducing apparatus, an optical element anda recording and reproducing method is also an object of the invention.

[0014] The above object can be attained by the following structures andmethods.

[0015] (1) An optical pickup apparatus for reproducing information froman optical information recording medium or for recording informationonto an optical information recording medium, comprises:

[0016] a first light source for emitting first light flux having a firstwavelength;

[0017] a second light source for emitting second light flux having asecond wavelength, the first wavelength being different from the secondwavelength;

[0018] a converging optical system having an optical axis and adiffractive portion, and

[0019] a photo detector;

[0020] wherein in case that the first light flux passes through thediffractive portion to generate at least one diffracted ray, an amountof n-th ordered diffracted ray of the first light flux is greater thanthat of any other ordered diffracted ray of the first light flux, and incase that the second light flux passes through the diffractive portionto generate at least one diffracted ray, an amount of n-th ordereddiffracted ray of the second light flux is greater than that of anyother ordered diffracted ray of the second light flux,

[0021] where n stands for an integer other than zero.

[0022] (2) An optical element for use in an optical pickup apparatus forreproducing information from an optical information recording medium orfor recoding information onto an optical information recording medium,comprises:

[0023] an optical axis, and

[0024] a diffractive portion,

[0025] wherein in case that the first light flux passes through thediffractive portion to generate at least one diffracted ray, an amountof n-th ordered diffracted ray of the first light flux is greater thanthat of any other ordered diffracted ray of the first light flux, and incase that the second light flux whose wavelength is different from thatof the first light flux passes through the diffractive portion togenerate at least one diffracted ray, an amount of n-th ordereddiffracted ray of the second light flux is greater than that of anyother ordered diffracted ray of the second light flux,

[0026] wherein a difference in wavelength between the first light fluxand the second light flux is 80 nm to 400 nm and n stands for an integerother than zero.

[0027] (3) An apparatus for reproducing information from an opticalinformation recording medium or for recording information onto theoptical information recording medium comprises;

[0028] an optical pickup apparatus, comprising

[0029] a first light source for emitting first light flux having a firstwavelength;

[0030] a second light source for emitting second light flux having asecond wavelength, the first wavelength being different from the secondwavelength;

[0031] a converging optical system having an optical axis, a diffractiveportion, and

[0032] a photo detector,

[0033] wherein

[0034] in case that the first light flux passes through the diffractiveportion to generate at least one diffracted ray, an amount of n-thordered diffracted ray of the first light flux is greater than that ofany other ordered diffracted ray of the first light flux, and in casethat the second light flux passes through the diffractive portion togenerate at least one diffracted ray, an amount of n-th ordereddiffracted ray of the second light flux is greater than that of anyother ordered diffracted ray of the second light flux, where n standsfor an integer other than zero.

[0035] (4) A method of reproducing information from or recordinginformation on at least two kinds of optical information recording mediaby an optical pickup apparatus comprising a first light source, a secondlight source, a photo detector and a converging optical system having anoptical axis and a diffractive portion, the method comprises steps of;

[0036] emitting first light flux from the first light source or secondlight flux from the second light flux, wherein a wavelength of thesecond light flux is different from a wavelength of the first lightflux;

[0037] letting the first light or the second light flux pass through thediffractive portion to generate at least one diffracted ray of the firstlight flux or a least one diffracted ray of the second light flux,wherein when an amount of n-th ordered diffracted ray among the at leastone diffracted ray of the first light flux is greater than an amount ofany other ordered diffracted ray of the first light flux, an amount ofn-th ordered diffracted ray among the at least one diffracted ray of thesecond light flux is greater than an amount of any other ordereddiffracted ray of the second light flux,

[0038] converging, by the converging optical system, the n-th ordereddiffracted ray of the first light flux onto a first informationrecording plane of a first optical information recording medium or then-th ordered diffracted ray of the second light flux onto a secondinformation recording plane of a second optical information recordingmedium in order for the optical pickup apparatus to record theinformation onto or reproduce the information from the first informationrecording plane or the second information recording plane,

[0039] detecting, by a photo detector, a first reflected light flux ofthe converged n-th ordered diffracted light from the first informationrecording plane or a second reflected light flux of the converged n-thordered diffracted light from the second information recording plane;

[0040] where n stands for an integer other than zero.

BRIEF DESCRIPTION OF THE DRAWINGS

[0041]FIG. 1 is a view of the optical path of a diffraction optical lensof Example 1 of the present invention.

[0042]FIG. 2 is a view of the spherical aberration to a wavelength λ=635nm by the diffraction optical lens of Example 1 of the presentinvention.

[0043]FIG. 3 is a view of the spherical aberration up to NA 0.45 to awavelength λ=780 nm by the diffraction optical lens of Example 1 of thepresent invention.

[0044]FIG. 4 is a view of the spherical aberration up to NA 0.60 to thewavelength λ=780 nm by the diffraction optical lens of Example 1 of thepresent invention.

[0045]FIG. 5 is a view of the wave front aberration to the wavelengthλ=635 nm by the diffraction optical lens of Example 1 of the presentinvention.

[0046]FIG. 6 is a view of the wave front aberration to the wavelengthλ=780 nm by the diffraction optical lens of Example 1 of the presentinvention.

[0047]FIG. 7 is a view of the optical path to the wavelength λ=405 nm bya diffraction optical lens of Example 2 of the present invention.

[0048]FIG. 8 is a view of the optical path to the wavelength λ=635 nm bythe diffraction optical lens of Example 2 of the present invention.

[0049]FIG. 9 is a view of the spherical aberration to the wavelengthλ=405 nm by the diffraction optical lens of Example 2 of the presentinvention.

[0050]FIG. 10 is a view of the spherical aberration to the wavelengthλ=635 nm by the diffraction optical lens of Example 2 of the presentinvention.

[0051]FIG. 11 is a view of the wave front aberration to the wavelengthλ=405 nm by the diffraction optical lens of Example 2 of the presentinvention.

[0052]FIG. 12 is a view of the wave front aberration to the wavelengthλ=635 nm by the diffraction optical lens of Example 2 of the presentinvention.

[0053]FIG. 13 is a view of the optical path to the wavelength λ=405 nmby a diffraction optical lens of Example 3 of the present invention.

[0054]FIG. 14 is a view of the optical path to the wavelength λ=635 nmby the diffraction optical lens of Example 3 of the present invention.

[0055]FIG. 15 is a view of the spherical aberration to the wavelengthλ=405 nm by the diffraction optical lens of Example 3 of the presentinvention.

[0056]FIG. 16 is a view of the spherical aberration to the wavelengthλ=635 nm by the diffraction optical lens of Example 3 of the presentinvention.

[0057]FIG. 17 is a view of the wave front aberration to the wavelengthλ=405 nm by the diffraction optical lens of Example 3 of the presentinvention.

[0058]FIG. 18 is a view of the wave front aberration to the wavelengthλ=635 nm by the diffraction optical lens of Example 3 of the presentinvention.

[0059]FIG. 19 is a view of the optical path by a diffraction opticallens of Example 4 of the present invention.

[0060]FIG. 20 is a view of the spherical aberrations to the wavelengthsλ=635 nm, 650 nm, and 780 nm by the diffraction optical lens of Example4 of the present invention.

[0061]FIG. 21 is a view of the optical path by a diffraction opticallens of Example 5 of the present invention.

[0062]FIG. 22 is a view of the spherical aberrations to the wavelengthsλ=635 nm, 650 nm, and 780 nm by the diffraction optical lens of Example5 of the present invention.

[0063]FIG. 23 is a view of the optical path to the wavelength λ=650 nm,by a diffraction optical lens of Example 6 of the present invention.

[0064]FIG. 24 is a view of the optical path to the wavelength λ=780 nm(NA=0.5), by the diffraction optical lens of Example 6 of the presentinvention.

[0065]FIG. 25 is a view of the spherical aberration up to the numeralaperture 0.60 to the wavelength λ=650±10 nm, by the diffraction opticallens of Example 6 of the present invention.

[0066]FIG. 26 is a view of the spherical aberration up to the numeralaperture 0.50 to the wavelength λ=780±10 nm, by the diffraction opticallens of Example 6 of the present invention.

[0067]FIG. 27 is a view of the spherical aberration up to the numeralaperture 0.60 to the wavelength λ=780 nm, by the diffraction opticallens of Example 6 of the present invention.

[0068]FIG. 28 is a view of the wave front aberration rms to thewavelength λ=650 nm, by the diffraction optical lens of Example 6 of thepresent invention.

[0069]FIG. 29 is a view of the wave front aberration rms to thewavelength λ=780 nm, by the diffraction optical lens of Example 6 of thepresent invention.

[0070]FIG. 30 is a view of the optical path to the wavelength λ=650 nm,by a diffraction optical lens of Example 7 of the present invention.

[0071]FIG. 31 is a view of the optical path to the wavelength λ=780 nm(NA=0.5), by the diffraction optical lens of Example 7 of the presentinvention.

[0072]FIG. 32 is a view of the spherical aberration up to the numeralaperture 0.60 to the wavelength λ=650±10 nm, by the diffraction opticallens of Example 7 of the present invention.

[0073]FIG. 33 is a view of the spherical aberration up to the numeralaperture 0.50 to the wavelength λ=780±10 nm, by the diffraction opticallens of Example 7 of the present invention.

[0074]FIG. 34 is a view of the spherical aberration up to the numeralaperture 0.60 to the wavelength λ=780 nm, by the diffraction opticallens of Example 7 of the present invention.

[0075]FIG. 35 is a view of the wave front aberration rms to thewavelength λ=650 nm, by the diffraction optical lens of Example 7 of thepresent invention.

[0076]FIG. 36 is a view of the wave front aberration rms to thewavelength λ=780 nm, by the diffraction optical lens of Example 7 of thepresent invention.

[0077]FIG. 37 is a view of the optical path to the wavelength λ=650 nm,by a diffraction optical lens of Example 8 of the present invention.

[0078]FIG. 38 is a view of the optical path to the wavelength λ=780 rim(NA=0.5), by the diffraction optical lens of Example 8 of the presentinvention.

[0079]FIG. 39 is a view of the spherical aberration up to the numeralaperture 0.60 to the wavelength λ=650±10 nm, by the diffraction opticallens of Example 8 of the present invention.

[0080]FIG. 40 is a view of the spherical aberration up to the numeralaperture 0.50 to the wavelength λ=780±10 nm, by the diffraction opticallens of Example 8 of the present invention.

[0081]FIG. 41 is a view of the spherical aberration up to the numeralaperture 0.60 to the wavelength λ=780 nm, by the diffraction opticallens of Example 8 of the present invention.

[0082]FIG. 42 is a view of the wave front aberration rms to thewavelength λ=650 nm, by the diffraction optical lens of Example 8 of thepresent invention.

[0083]FIG. 43 is a view of the wave front aberration rms to thewavelength λ=780 nm, by the diffraction optical lens of Example 8 of thepresent invention.

[0084]FIG. 44 is a graph showing the relationship of the number of thediffraction annular bands and the height from the optical axis of thediffraction optical lens of the Example 6 of the present invention.

[0085]FIG. 45 is a graph showing the relationship of the number of thediffraction annular bands and the height from the optical axis of thediffraction optical lens of the Example 7 of the present invention.

[0086]FIG. 46 is a graph showing the relationship of the number of thediffraction annular bands and the height from the optical axis of thediffraction optical lens of the Example 8 of the present invention.

[0087]FIG. 47 is a view typically showing the relationship of thediffraction lens power and the lens shape of the diffraction opticallens according to Examples of the present invention.

[0088]FIG. 48 is a view of the optical path showing the structure of theoptical pickup apparatus according to the second embodiment of thepresent invention.

[0089]FIG. 49 is a view of the optical path showing the structure of theoptical pickup apparatus according to the third embodiment of thepresent invention.

[0090]FIG. 50 is a view of the optical path to the wavelength λ=650 nmof the objective lens in Example 9 of the present invention.

[0091]FIG. 51 is a view of the optical path to the wavelength λ=780 nmof the objective lens in Example 9 of the present invention.

[0092]FIG. 52 is a view of the spherical aberration to the wavelengthλ=650 nm of the objective lens of Example 9 of the present invention.

[0093]FIG. 53 is a view of the spherical aberration up to NA 0.45 to thewavelength λ=780 nm of the objective lens of Example 9 of the presentinvention.

[0094]FIG. 54 is a view of the spherical aberration up to 0.60 to thewavelength λ=780 nm of the objective lens of Example 9 of the presentinvention.

[0095]FIG. 55 is a view of the wave front aberration to the wavelengthλ=650 nm of the objective lens of Example 9 of the present invention.

[0096]FIG. 56 is a view of the wave front aberration to the wavelengthλ=780 nm of the objective lens of Example 9 of the present invention.

[0097]FIG. 57 is a view of the optical path to the wavelength λ=650 nmof the objective lens of Example 10 of the present invention.

[0098]FIG. 58 is a view of the optical path to the wavelength λ=400 nmof the objective lens of Example 10 of the present invention.

[0099]FIG. 59 is a view of the optical path to the wavelength λ=780 nmof the objective lens of Example 10 of the present invention.

[0100]FIG. 60 is a view of the spherical aberration to the wavelengthλ=650 nm of the objective lens of Example 10 of the present invention.

[0101]FIG. 61 is a view of the spherical aberration to the wavelengthλ=400 nm of the objective lens of Example 10 of the present invention.

[0102]FIG. 62 is a view of the spherical aberration up to NA 0.45 to thewavelength λ=780 nm of the objective lens of Example 10 of the presentinvention.

[0103]FIG. 63 is a view of the spherical aberration up to NA 0.65 to thewavelength λ=780 nm of the objective lens of Example 10 of the presentinvention.

[0104]FIG. 64 is a view of the wave front aberration to the wavelengthλ=650 nm of the objective lens of Example 10 of the present invention.

[0105]FIG. 65 is a view of the wave front aberration to the wavelengthλ=400 nm of the objective lens of Example 10 of the present invention.

[0106]FIG. 66 is a view of the wave front aberration to the wavelengthλ=780 nm of the objective lens of Example 10 of the present invention.

[0107]FIG. 67 is a view showing the structure of the optical pickupapparatus according to Embodiment 4 of the present invention.

[0108]FIG. 68 is a view of the optical path to the wavelength λ=650 nmof the objective lens of Example 11 of the present invention.

[0109]FIG. 69 is a view of the optical path to the wavelength λ=400 rimof the objective lens of Example 11 of the present invention.

[0110]FIG. 70 is a view of the optical path to the wavelength λ=780 nmof the objective lens of Example 11 of the present invention.

[0111]FIG. 71 is a view of the spherical aberration to the wavelengthλ=650 nm of the objective lens of Example 11 of the present invention.

[0112]FIG. 72 is a view of the spherical aberration to the wavelengthλ=400 nm of the objective lens of Example 11 of the present invention.

[0113]FIG. 73 is a view of the spherical aberration up to the numericalaperture 0.45 to the wavelength λ=780 nm of the objective lens ofExample 11 of the present invention.

[0114]FIG. 74 is a view of the spherical aberration up to the numericalaperture 0.65 to the wavelength λ=780 nm of the objective lens ofExample 11 of the present invention.

[0115]FIG. 75 is a view of the wave front aberration to the wavelengthλ=650 nm of the objective lens of Example 11 of the present invention.

[0116]FIG. 76 is a view of the wave front aberration to the wavelengthλ=400 nm of the objective lens of Example 11 of the present invention.

[0117]FIG. 77 is a view of the wave front aberration to the wavelengthλ=780 nm of the objective lens of Example 11 of the present invention.

[0118]FIG. 78 is a view of the optical path to the wavelength λ=650 nmof the objective lens of Example 12 of the present invention.

[0119]FIG. 79 is a view of the optical path to the wavelength λ=400 nmof the objective lens of Example 12 of the present invention.

[0120]FIG. 80 is a view of the optical path to the wavelength λ=780 nmof the objective lens of Example 12 of the present invention.

[0121]FIG. 81 is a view of the spherical aberration to the wavelengthλ=650 nm of the objective lens of Example 12 of the present invention.

[0122]FIG. 82 is a view of the spherical aberration to the wavelengthλ=400 nm of the objective lens of Example 12 of the present invention.

[0123]FIG. 83 is a view of the spherical aberration up to the numericalaperture 0.45 to the wavelength λ=780 nm of the objective lens ofExample 12 of the present invention.

[0124]FIG. 84 is a view of the spherical aberration up to the numericalaperture 0.65 to the wavelength λ=780 nm of the objective lens ofExample 12 of the present invention.

[0125]FIG. 85 is a view of the wave front aberration to the wavelengthλ=650 nm of the objective lens of Example 12 of the present invention.

[0126]FIG. 86 is a view of the wave front aberration to the wavelengthλ=400 nm of the objective lens of Example 12 of the present invention.

[0127]FIG. 87 is a view of the wave front aberration to the wavelengthλ=780 nm of the objective lens of Example 12 of the present invention.

[0128]FIG. 88 is a view of the optical path to the wavelength λ=650 nmof the objective lens of Example 13 of the present invention.

[0129]FIG. 89 is a view of the optical path to the wavelength λ=400 nmof the objective lens of Example 13 of the present invention.

[0130]FIG. 90 is a view of the optical path to the wavelength λ=780 nmof the objective lens of Example 13 of the present invention.

[0131]FIG. 91 is a view of the spherical aberration to the wavelengthλ=650 nm of the objective lens of Example 13 of the present invention.

[0132]FIG. 92 is a view of the spherical aberration to the wavelengthλ=400 nm of the objective lens of Example 13 of the present invention.

[0133]FIG. 93 is a view of the spherical aberration up to the numericalaperture 0.45 to the wavelength λ=780 nm of the objective lens ofExample 13 of the present invention.

[0134]FIG. 94 is a view of the spherical aberration up to the numericalaperture 0.65 to the wavelength λ=780 nm of the objective lens ofExample 13 of the present invention.

[0135]FIG. 95 is a view of the wave front aberration to the wavelengthλ=650 nm of the objective lens of Example 13 of the present invention.

[0136]FIG. 96 is a view of the wave front aberration to the wavelengthλ=400 nm of the objective lens of Example 13 of the present invention.

[0137]FIG. 97 is a view of the wave front aberration to the wavelengthλ=780 nm of the objective lens of Example 13 of the present invention.

[0138]FIG. 98 is a view of the optical path to the wavelength λ=400 nm,of the objective lens of Example 13 of the present invention.

[0139]FIG. 99 is a view of the spherical aberration to the wavelengthλ=400 nm±10 nm, of the objective lens of Example 13 of the presentinvention.

[0140]FIG. 100 is a view of the spherical aberration to the wavelengthλ=650 nm±10 nm, of the objective lens of Example 13 of the presentinvention.

[0141]FIG. 101 is a view of the spherical aberration to the wavelengthλ=780 nm±10 nm, of the objective lens of Example 13 of the presentinvention.

[0142]FIG. 102 is a view of the optical path showing the first structureof the optical pickup apparatus according to Embodiment 8 of the presentinvention.

[0143]FIG. 103 is a view of the optical path showing the secondstructure of the optical pickup apparatus according to Embodiment 8 ofthe present invention.

[0144]FIG. 104 is a view of the optical path showing the third structureof the optical pickup apparatus according to Embodiment 8 of the presentinvention.

[0145]FIG. 105 is a view of the optical path showing the fourthstructure of the optical pickup apparatus according to Embodiment 8 ofthe present invention.

[0146]FIG. 106 is a view of the optical path showing the fifth structureof the optical pickup apparatus according to Embodiment 8 of the presentinvention.

[0147]FIG. 107 is a view of the optical path showing the sixth structureof the optical pickup apparatus according to Embodiment 8 of the presentinvention.

[0148]FIG. 108 is a view of the optical path showing the seventhstructure of the optical pickup apparatus according to Embodiment 8 ofthe present invention.

[0149]FIG. 109 is a typical view showing the structure of the opticaldisk of Super RENS system.

[0150]FIG. 110 is a graph showing the relationship of the imageformation magnification m2 and the wave front aberration of theobjective lens of the Example 15 according to Embodiment 8 of thepresent invention.

[0151]FIG. 111 is a sectional view of Example 15 according to Embodiment8 of the present invention.

[0152]FIG. 112 is a view of the spherical aberration of Example 15.

[0153]FIG. 113 is an illustration of an action of the diffractionpattern.

[0154]FIG. 114 is a typical view showing an influence of the chromaticaberration on the spherical aberration of the objective lens accordingto Embodiment 8 of the present invention.

[0155]FIG. 115 is a typical view showing an influence of +first ordereddiffraction on the spherical aberration of the objective lens accordingto Embodiment 8 of the present invention.

[0156]FIG. 116 is a typical view showing an influence of −first ordereddiffraction on the spherical aberration of the objective lens accordingto Embodiment 8 of the present invention.

[0157]FIG. 117 is a view of the optical path showing the structure ofthe optical pickup apparatus according to Embodiment 7 of the presentinvention.

[0158]FIG. 118 is a view of the optical path of the diffraction opticallens (the objective lens having the diffraction surface) which is theobjective lens of Example 15 according to Embodiment 7 of the presentinvention.

[0159]FIG. 119 is a view of the spherical aberration up to the numericalaperture 0.60 to the wavelengths (λ)=640, 650, 660 nm of the diffractionoptical lens in FIG. 118.

[0160]FIG. 120 is a view of the optical path of the diffraction opticallens in the case where the thickness of the transparent substrate of theoptical information medium is larger than that in FIG. 118, in Example15.

[0161]FIG. 121 is a view of the spherical aberration up to the numericalaperture 0.60 to the wavelength λ=770, 780, 790 nm of the diffractionoptical lens in FIG. 120.

[0162]FIG. 122 is a view of the optical path of the diffraction opticallens (the objective lens having the diffraction surface) which is theobjective lens in Example 16 according to Embodiment 7 of the presentinvention.

[0163]FIG. 123 is a view of the spherical aberration up to the numericalaperture 0.60 to the wavelength (λ)=640, 650, 660 nm of the diffractionoptical lens in FIG. 122.

[0164]FIG. 124 is a view of the optical path of the diffraction opticallens in the case where the thickness of the transparent substrate of theoptical information medium is larger than that in FIG. 122, in Example16.

[0165]FIG. 125 is a view of the spherical aberration up to the numericalaperture 0.60 to the wavelength (λ)=770, 780, 790 nm of the diffractionoptical lens in FIG. 124.

[0166]FIG. 126 is a view of the optical path of the diffraction opticallens (the objective lens having the diffraction surface) which is theobjective lens in Example 17 according to Embodiment 7 of the presentinvention.

[0167]FIG. 127 is a view of the spherical aberration up to the numericalaperture 0.60 to the wavelength (λ)=640, 650, 660 nm of the diffractionoptical lens in FIG. 126.

[0168]FIG. 128 is a view of the optical path of the diffraction opticallens in the case where the thickness of the transparent substrate of theoptical information medium is larger than that in FIG. 126, in Example17.

[0169]FIG. 129 is a view of the spherical aberration up to the numericalaperture 0.60 to the wavelength (λ)=770, 780, 790 nm of the diffractionoptical lens in FIG. 128.

[0170]FIG. 130 is a view of the optical path of the diffraction opticallens (the objective lens having the diffraction surface) which is theobjective lens in Example 18 according to Embodiment 7 of the presentinvention.

[0171]FIG. 131 is a view of the spherical aberration up to the numericalaperture 0.70 to the wavelength (λ)=390, 400, 410 nm of the diffractionoptical lens in FIG. 130.

[0172]FIG. 132 is a view of the optical path of the diffraction opticallens in the case where the thickness of the transparent substrate of theoptical information medium is larger than that in FIG. 130, in Example18.

[0173]FIG. 133 is a view of the spherical aberration up to the numericalaperture 0.70 to the wavelength λ=640, 650, 660 nm of the diffractionoptical lens in FIG. 132.

[0174]FIG. 134 is an illustration showing a cross sectional view of adiffractive annular band.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0175] An optical pickup apparatus for reproducing information from anoptical information recording medium or for recording information ontoan optical information recording medium has therein a first light sourcefor emitting first light flux having a first wavelength, a second lightsource for emitting second light flux having a second wavelength, thefirst wavelength being different from the second wavelength, aconverging optical system having an optical axis, a diffractive portion,and a photo detector. Further, the diffractive portion generates moren-th ordered diffracted ray than other ordered diffracted ray in thefirst light flux which has passed the diffractive portion, and generatesmore n-th ordered diffracted ray than other ordered diffracted ray alsoin the second light flux which has passed the diffractive portion. nstands for an integer other than zero. The optical element of theinvention is one having a diffraction portion which makes the aforesaidembodiment possible. An apparatus for reproducing information from anoptical information recording medium or for recording information ontothe optical information recording medium has the optical pickupapparatus stated above.

[0176] (11-1)

[0177] Incidentally, “an amount of n-th ordered diffracted ray beinggreater than that of any other ordered diffracted ray 11” means that thediffraction efficiency for the n-th ordered diffracted ray is higherthan that for the other ordered diffracted ray other than the n-thordered diffracted ray. Further, n in n-th ordered includes also a sign,and when +first ordered diffracted ray is generated more than otherordered diffracted ray in the first light flux which has passed thediffractive portion, it is intended that +first ordered diffracted rayis generated more than other ordered diffracted ray even in the secondlight flux which has passed the diffractive portion, and it does notinclude that −first ordered diffracted ray is generated more than otherordered diffracted ray in the second light flux which has passed thediffractive portion.

[0178] (11-2)

[0179] The optical pickup apparatus of the invention is one wherein onepickup apparatus can conduct recording and/or reproducing opticalinformation recording media in different types employing at least twowavelengths each being different from others. Namely, the optical pickupapparatus of the invention is one used for recording/reproducing ofdifferent information recording media such as a first opticalinformation recording medium and a second optical information recordingmedium. A first light source of the optical pickup apparatus emits firstlight flux for reproducing information from a first optical informationrecording medium or for recording information onto the first opticalinformation recording medium, while, a second light source of theoptical pickup apparatus emits second light flux for reproducinginformation from a second optical information recording medium or forrecording information onto the second optical information recordingmedium. Usually, an optical information recording medium has atransparent substrate on an information recording plane.

[0180] (11-3)

[0181] When putting the function of the invention in another way, theconverging optical system is capable of converging “n-th ordereddiffracted ray of the first light flux”, which is generated at thediffractive portion by the first light flux being reached thediffractive portion, on a first information recording plane of the firstoptical information recording medium through a first transparentsubstrate, to reproduce information recorded in the first opticalinformation recording medium or to record information onto the firstoptical information recording medium, and the converging optical systemis capable of converging “n-th ordered diffracted ray in the secondlight flux”, which is generated at the diffractive portion by the secondlight flux being reached the diffractive portion, on a secondinformation recording plane of the second optical information recordingmedium through a second transparent substrate, to reproduce informationrecorded in the second optical information recording medium or to recordinformation onto the second optical information recording medium, andthe photo detector is capable of receiving light flux reflected from thefirst information recording plane or the second information recordingplane.

[0182] (11-4)

[0183] There will be shown as follows the embodiment which is morepreferable, wherein the converging optical system is capable ofconverging n-th ordered diffracted ray in the first light flux on afirst information recording plane of the first optical informationrecording medium under the state that wave-front aberration is notlarger than 0.07 λrms within the prescribed numerical aperture of thefirst optical information recording medium in the first light flux onthe image side of the objective lens (in other words, under the statewherein the light flux within the prescribed numerical aperture takesdiffraction limit capacity or less in the best image point (bestfocus)), and the converging optical system is capable of converging n-thordered diffracted ray in the second light flux on a second informationrecording plane of the second optical information recording medium underthe state that wave-front aberration is not larger than 0.07 λrms withinthe prescribed numerical aperture of the second optical informationrecording medium in the second light flux on the image side of theobjective lens (in other words, under the state wherein the light fluxwithin the prescribed numerical aperture takes diffraction limitcapacity or less in the best image point (best focus)).

[0184] Further, it is preferable that n-th ordered diffracted ray isconverged under the state that wave-front aberration is not larger than0.07 λrms within the prescribed numerical aperture on the image side ofthe objective lens on each information recording plane, even in the caseof wavelength shift of about ±10 nm or less caused by temperaturefluctuation and electric current fluctuation, in the first light sourceor in the second light source. In particular, it is especiallypreferable that n-th ordered diffracted ray is converged under the stateof 0.07 arms or less within the prescribed numerical aperture on theimage side of the objective lens, even when the first light flux or thesecond light flux is one having a wavelength of 600 nm or less (forexample, 350 nm-480 nm) and wavelength shifting of about ±10 nm or lessis generated.

[0185] (11-5)

[0186] Incidentally, when n-th ordered diffracted ray is +first ordereddiffracted ray or −first ordered diffracted ray, a loss of a quantity oflight is less than that in an occasion where a diffracted ray of higherordered than ±first ordered is used, which is preferable.

[0187] Further, when a diffraction efficiency of n-th ordered diffractedray of the first light flux in the diffractive portion is represented byA% and a diffraction efficiency of diffracted ray of other certain-thordered (preferably, the number of ordered with the greatest diffractionefficiency among number of ordered other than n) is represented by B%,it is preferable to satisfy A−B≧10, while, when a diffraction efficiencyof n-th ordered diffracted ray of the second light flux in thediffractive portion is represented by A′% and a diffraction efficiencyof diffracted ray of other certain-th ordered is represented by B′%, itis preferable to satisfy A′−B′≧10. The condition of A−B≧30 and A′−B′≧30is more preferable, that of A−B≧50 and A′−B′≧50 is still morepreferable, and that of A−B ≧70 and A′−B′≧70 is further more preferable.

[0188] (11-6)

[0189] When both of the first light flux and second light flux are usedfor recording of information on optical information recording medium, itis preferable that diffraction efficiency of n-th ordered diffracted rayin the diffractive portion is made to be maximum at the wavelengthbetween the wavelength of the first light flux and the wavelength of thesecond light flux.

[0190] (11-7)

[0191] When either of the first light flux and second light flux aloneis used for recording of information on optical information recordingmedium and the other light flux is used for reproduction only, it ispreferable that diffraction efficiency of n-th ordered diffracted ray inthe diffractive portion is made to be minimum at the wavelength betweenthe wavelength of the first light flux and the wavelength of the secondlight flux. The more preferable is that the diffraction efficiency ofthe n-th ordered diffracted ray in the diffractive portion is made to bemaximum at one of the wavelength of the first light flux and thewavelength of the second light flux in using for recording ofinformation.

[0192] (11-8)

[0193] As an optical element on which the diffractive portion isprovided, a lens having a refraction surface and a flat type elementboth provided on the converging optical system are given, though thereis no limitation in particular.

[0194] When a lens having a refraction surface as an optical element onwhich a diffractive portion is provided, there are given an objectivelens, a collimator lens and a coupling lens as a concrete example of theoptical element. On the refraction surfaces on each of these lenses, adiffractive portion can be provided. A flat-shaped or lens-shapedoptical element which is intended only to be provided with a diffractiveportion may also be added to a converging optical system.

[0195] Incidentally, when providing a diffraction portion on arefraction surface of an objective lens, it is preferable that anoutside diameter of the objective lens (outside diameter including aflange if the flange is provided) is larger than an aperture diameter by0.4 mm-2 mm.

[0196] (11-9)

[0197] The diffractive portion may be provided either on an opticalsurface of the optical element on the light source side, or on the imageside (optical information recording medium side), or on both sides.Further, the diffractive portion may be provided either on the convexsurface or on the concave surface.

[0198] (11-10)

[0199] When a diffractive portion is provided on an objective lens, itis more preferable because the number of parts is reduced and errors inassembly of an optical pickup apparatus in manufacturing can be reduced.In that case, it is preferable that the objective lens is of asingle-element type, but it may also be of a two-element type. A plasticlens is preferable, but a glass lens is also acceptable. It is alsopossible to provide on the surface of a glass lens a resin layer onwhich a diffractive portion is formed. It is preferable that theobjective lens on which the diffractive portion is provided has on itsouter circumference a flange section having a surface extending in thedirection perpendicular to an optical axis. This makes it easy to mounton the pickup apparatus accurately, and makes it possible to obtainstable performance even when ambient temperature fluctuates. It isfurther preferable that the refraction surface of the objective lens isan aspheric surface and a diffractive portion is provided on theaspheric surface. The diffractive portion may naturally be providedeither on one side of the objective lens or on both sides thereof.

[0200] (11-11)

[0201] Further, it is preferable that an optical element on which adiffractive portion is provided is made of a material with Abbe's numberνd of not less than 50 and not more than 100. It may either be made ofplastic or be made of glass. Incidentally, in the case of a plasticlens, it is preferable that a refractive index of its material is in arange of 1.4-1.75, and the range of 1.48-1.6 is more preferable and thatof 1.5-1.56 is further preferable.

[0202] When the diffractive portion is provided on a lens (preferably ona plastic lens), it is preferable that the following conditionalexpression is satisfied, for obtaining an optical pickup apparatus andan optical element which are stable against temperature fluctuation.

−0.0002/° C.<Δn/ΔT<−0.00005° C.

[0203] wherein,

[0204] ΔT: Temperature fluctuation

[0205] Δn: Amount of change of refractive index of the lens

[0206] It is further preferable to satisfy the following conditionalexpression.

0.05 nm/° C.<Δλ1/ΔT<0.5 nm/° C.

[0207] wherein,

[0208] Δλ1 (nm): Amount of change of wavelength of first light sourcefor temperature fluctuation ΔT

[0209] (11-12)

[0210] The diffractive portion is preferably a phase type one from theviewpoint of efficiency of using light, though it may also be anamplitude type one. It is preferable that the diffractive pattern of thediffractive portion is shaped to be symmetry rotatable in relation tothe optical axis. It is preferable that the diffractive portion hasplural annular bands when viewed in the direction of the optical axis,and these plural annular bands are formed mostly on the concentriccircle whose center is on the optical axis or in the vicinity of theoptical axis. A circle is preferable, but it may also be an ellipse. Ablaze type ring-zonal diffraction surface having steps is especiallypreferable. It may further be a ring-zonal diffraction surface which isformed stepwise. It may further be a ring-zonal diffraction surfacewhich is formed stepwise as annular bands which shift discretely in thedirection where lens thickness is greater as its position becomes moredistant from the optical axis. Incidentally, it is preferable that thediffractive portion is ring-zonal, but it may also be a 1-dimensionaldiffraction grating.

[0211] (11-13)

[0212] When the diffraction portion represents concentric circles in aring-zonal form, a pitch of diffraction annular bands is defined by theuse of a phase difference function or an optical path differencefunction. In this case, it is preferable that a coefficient other thanzero is owned by at least one term other than a squared term in a phasedifference function expressed by a power series which shows positions ofplural annular bands. Due to this structure, it is possible to correctspherical aberration of chromatic aberration caused by rays of lighteach having a different wavelength.

[0213] (11-14)

[0214] When a coefficient other than zero is owned by a squared term ina phase difference function expressed by a power series which showspositions of plural annular bands of the diffractive portion, paraxialchromatic aberration can be corrected, which is preferable. However,when it is important not to make a pitch of diffraction annular bands tobe too small, it is also possible to make the phase difference functionexpressed by a power series which shows positions of plural annularbands of the diffractive portion to include no squared term.

[0215] (11-15)

[0216] Incidentally, it is preferable that the number of steps ofdiffraction annular bands of the diffractive portion is in a range from2 to 45. The more preferable is not more than 40. Still furtherpreferable is not more than 15. Incidentally, counting of the number ofsteps is achieved by counting the number of stepped sections of annularbands.

[0217] Further, it is preferable that a depth of the stepped section ofdiffraction annular bands of the diffraction portion in the direction ofthe optical axis is not more than 2 μm. Due to this structure, anoptical element can be manufactured easily, and n-th ordered diffractedray can easily be made to be+first ordered diffracted ray or −firstordered diffracted ray.

[0218] Further, when providing a diffraction portion on the surface ofan optical element on the light source side, it is preferable that adepth of a stepped section becomes greater as the stepped sectionbecomes more distant from an optical axis.

[0219] (11-16)

[0220] With regard to the effect of the diffractive portion to deflectthe light flux, in the present specification, the case that the lightflux is deflected toward the optical axis is called as the positiveeffect, on the other hand, the case that the light flux is deflected soas to be shifted away from the optical axis is called as the negativeeffect.

[0221] With regard to the pitch on the ring-zonal diffraction surface,there may also be provided a pitch wherein a pitch is provided to beinversely proportional to a height from an optical axis. It is alsopossible to provide a pitch having aspheric characteristics wherein theway of providing a pitch is not inversely proportional to a height froman optical axis.

[0222] In particular, when providing a pitch having asphericcharacteristics, namely, when a pitch is not provided to be inverselyproportional to a height from an optical axis, it is preferable thatthere is no point of inflection in the function of optical pathdifference, though there may also be the point of inflection.

[0223] Further, the diffraction effect added in the diffractive portionmay either be positive on the entire surface of the diffractive portion,or be negative on the entire surface of the diffractive portion. It isalso possible to arrange so that a plus or minus sign of the diffractioneffect added in the diffractive portion is switched at least one time inthe direction to become more distant from the optical axis in thedirection perpendicular to the optical axis. For example, there is givena type wherein a sign is changed from minus to plus in the direction tobecome more distant from the optical axis in the direction perpendicularto the optical axis, as shown in FIG. 47(c). In other words, it can besaid that plural annular bands of the diffractive portion are blazed,and on the diffractive annular band closer to the optical axis, itsstepped section is positioned to be away from the optical axis, and onthe diffractive annular band farther from the optical axis, its steppedsection is positioned to be closer to the optical axis. There can alsobe given a type wherein a sign is changed from plus to minus in thedirection to become more distant from the optical axis in the directionperpendicular to the optical axis, as shown in FIG. 47(d). In otherwords again, it can be said that plural annular bands of the diffractiveportion are blazed, and on the aforesaid diffractive annular band closerto the optical axis, its stepped section is positioned to be closer tothe optical axis, and on the diffractive annular band farther from theoptical axis, its stepped section is positioned to be farther from theoptical axis.

[0224] Incidentally, the pitch (zone distance) of diffraction annularbands means distance p in FIG. 134 between a step of a annular band anda step of its adjacent annular band in the direction perpendicular tothe optical axis, while, a depth of the step means length d in FIG. 134of the step in the optical direction.

[0225] (11-17)

[0226] Incidentally, when the pitch is smaller, converging effect anddiverging effect on that portion become stronger, and when pitch isgreater, converging effect and diverging effect on that portion becomeweaker

[0227] Further, the diffractive portion may also be provided on theentire portion of the surface through which a light flux passes, in anoptical element having a diffractive portion. In other words, it can besaid that it is also possible to arrange so that the all light fluxwithin the maximum numerical aperture at an image side of an objectivelens may pass through the diffractive portion. A diffractive portion mayalso be provided simply on the entire portion on one optical surface ofan optical element, or not less than 70% (not less than 80% ispreferable and not less than 90% is more preferable) of one opticalsurface of the optical element may be made to be a diffractive portion.

[0228] (11-18)

[0229] Further, the diffractive portion may also be provided on only apart of the surface of an optical element through which a light fluxpasses, to make another area to be a refraction surface or atransmission surface, in an optical element. When a diffractive portionis provided only on a part of the surface through which a light fluxpasses, the diffractive portion may be provided only on a portion in thevicinity of an optical axis including the optical axis, or thediffractive portion may be provided to be in a ring shape, without beingprovided to be in the vicinity of the optical axis. For example, adiffractive portion may be provided on 10% or more and less than 90% ofone surface in optical surfaces of an optical element. Or, 10% or moreand less than 50% of one surface may be made to be a diffractiveportion.

[0230] (11-19)

[0231] Incidentally, when providing a diffractive portion only on a partof the surface of an optical element through which a light flux passes,NA1>NAH1, NAH1≧NA2, NA2≧NAL1≧0 is preferable in the case of NA1>NA2. Inthe case of NA2>NA1, NA2>NAH2, NAH2≧NA1, NA1≧NAL2≧0 is preferable.Incidentally, each of NA1 and NA2 is a prescribed numerical aperture ofan objective lens on the image side, when using the first light flux andthe second light flux respectively. Each of NAH1 and NAH2 is a numericalaperture of the objective lens on the image side for each of the firstlight flux and the second light flux passing through the outermost sideof the diffractive portion. Each of NAL1 and NAL2 is a numericalaperture of the objective lens on the image side for each of the firstlight flux and the second light flux passing through the innermost sideof the diffractive portion.

[0232] (11-20)

[0233] When the diffractive portion is provided only on a part of thesurface of an optical element through which a light flux passes, it ispreferable that the light flux which has passed the diffraction portionat NA1 or less in the first light flux and light which has passed therefraction surface at NA1 or less other than the diffractive portion areconverged at mostly the same position, in the case of NA1>NA2. In thecase of NA2>NA1, it is preferable that the light flux which has passedthe diffraction portion at NA2 or less in the second light flux andlight which has passed the refraction surface at NA2 or less other thanthe diffractive portion are converged at mostly the same position.

[0234] An embodiment wherein the diffractive portion has the firstdiffraction pattern and the second diffraction pattern, and the seconddiffraction pattern is farther than the first diffraction pattern interms of a distance from the optical axis. It is possible to combine adiffractive portion and a refraction surface having no diffractiveportion on the same plane.

[0235] (11-21)

[0236] When two types of diffraction patterns are used, it is alsopossible to arrange so that n-th ordered diffracted ray is generatedmore than other ordered diffracted ray in the first light flux which haspassed the first diffraction pattern of the diffractive portion and iscapable to be converged on a first information recording plane, and n-thordered diffracted ray is generated more than other ordered diffractedray also in the second light flux which has passed the first diffractionpattern of the diffractive portion and is capable to be converged on asecond information recording plane, and n-th ordered diffracted ray isgenerated more than other ordered diffracted ray in the first light fluxwhich has passed the second diffraction pattern of the diffractiveportion and is capable to be converged on a first information recordingplane, while, 0-th ordered light representing transmitted light isgenerated more than other ordered diffracted ray in the second lightflux which has passed the second diffraction pattern of the diffractiveportion. The n-th ordered in this case is preferably first ordered.

[0237] (11-22)

[0238] Further, in another embodiment, n-th ordered diffracted ray isgenerated more than other ordered diffracted ray in the first light fluxwhich has passed the first diffraction pattern of the diffractiveportion and is capable to be converged on a first information recordingplane, and n-th ordered diffracted ray is generated more than otherordered diffracted ray also in the second light flux which has passedthe first diffraction pattern of the diffractive portion and is capableto be converged on a second information recording plane, and 0-thordered diffracted ray is generated more than other ordered diffractedray in the first light flux which has passed the second diffractionpattern of the diffractive portion and is capable to be converged on afirst information recording plane, while, diffracted ray not of n-thordered but of negative ordered is generated more than other ordereddiffracted ray in the second light flux which has passed the seconddiffraction pattern of the diffractive portion. The n-th ordered in thiscase is preferably +first ordered, and negative ordered is preferably−first ordered.

[0239] (11-23)

[0240] In the case of an optical pickup apparatus or an optical elementused in plural optical information recording media each having adifferent thickness of a transparent substrate, it is especiallypreferable that a pitch of annular bands of the diffraction portionsatisfies the following conditional expression.

0.4<=|(Ph/Pf)−2|<=25

[0241] The more preferable is 0.8≦|(Ph/Pf)−2|≦6, and further preferableis 1.2≦|(Ph/Pf)−2|≦2

[0242] (11-24)

[0243] A pitch of annular bands of the diffractive portion correspondingto the maximum numerical aperture of the objective lens on the imageside is represented by Pf, and a pitch of annular bands of thediffractive portion corresponding to ½ of the maximum numerical apertureis represented by Ph. Incidentally, with regard to the maximum numericalaperture, the greatest one among prescribed numerical apertures of sometypes of optical information recording media subjected to informationreading/recording in an optical pickup apparatus is regarded as themaximum numerical aperture. Incidentally, the prescribed numericalaperture means a numerical aperture which makes reading/recording ofinformation on optical information recording medium by a light fluxwhich has a prescribed wavelength possible in its optical pickupapparatus, but it may also be a numerical aperture stipulated by thestandard of a certain optical information recording medium. Further, “apitch of annular bands of the diffractive portion corresponding to themaximum numerical aperture of the objective lens on the image side”means a pitch of annular bands located at the outermost portion of thelight flux passing through the diffraction portion in the case of themaximum numerical aperture. “A pitch of annular bands of the diffractiveportion corresponding to ½ of the maximum numerical aperture” means apitch of annular bands located at the outermost portion of the lightflux passing through the diffraction portion in the case of thenumerical aperture which is a half of the maximum numerical aperture.

[0244] (11-25)

[0245] Incidentally, there will be accepted an optical pickup apparatuswherein up to the prescribed numerical aperture is made to beno-aberration for one light flux among two light fluxes respectivelyfrom two light sources, and for the portion outside the prescribednumerical aperture, aberration is made to be flare.

[0246] (11026)

[0247] In other words, it can be said as follows. The first light fluxwhich is within a prescribed numerical aperture, of a first opticalinformation recording medium, of the objective lens on the image side inthe case of using a first light flux is converged on a first informationrecording plane of the first optical information recording medium underthe state of 0.07 λrms or less, and the first light flux passing throughthe outside of the prescribed numerical aperture of the objective lenson the image side in the case of using a first light flux is made to begreater than 0.07 λrms on a first information recording plane, and thesecond light flux passing through the prescribed numerical aperture ofthe objective lens on the image side in the case of using a first lightflux as well as the second light flux passing through the outside of theaforesaid numerical aperture are converged on a second informationrecording plane under the state of 0.07 λrms or less. In this case, NA1is smaller than NA2, and a light flux between NA1 and NA2 is made to beflare when recording and reproducing the first optical informationrecording medium.

[0248] (11-27)

[0249] Or, the second light flux which is within a prescribed numericalaperture, of a second optical information recording medium, of theobjective lens on the image side in the case of using a second lightflux is converged on a second information recording plane of the secondoptical information recording medium under the state of 0.07 arms orless, and the second light flux passing through the outside of aprescribed numerical aperture of the objective lens on the image side inthe case of using a second light flux is made to be greater than 0.07λrms on a second information recording plane, and the first light fluxpassing through the prescribed numerical aperture of the objective lenson the image side in the case of using a second light flux as well asthe first light flux passing through the outside of the aforesaidnumerical aperture are converged on a first information recording planeunder the state of 0.07 λrms or less. In this case, NA1 is greater thanNA2, and a light flux between NA2 and NA1 is made to be flare, whenrecording and reproducing the second optical information recordingmedium.

[0250] These embodiments can be established voluntarily by the design ofa diffraction portion. For example, it is possible either to provide adiffractive portion on the entire surface of an optical element andthereby to generate flare at the prescribed numerical aperture or moreby designing the diffractive portion, or to provide a diffractiveportion on a part of the surface of an optical element and to make theother part to be a refraction surface so that flare may be generated bythe refraction surface and the diffractive portion.

[0251] (11-28)

[0252] In the embodiment to generate flare stated above, it ispreferable that an aperture regulating means to block or diffract thefirst light flux outside a prescribed numerical aperture of theobjective lens on the image side in the case of using the first lightflux and to transmit the second light flux and an aperture regulatingmeans to block or diffract the second light flux outside a prescribednumerical aperture of the objective lens on the image side in the caseof using the second light flux and to transmit the first light flux arenot provided. Namely, it is preferable to provide an ordinary apertureonly without providing a dichroic filter or a hologram filter. If thediffractive portion is only designed to satisfy the aforesaid function,it is enough to provide only an ordinary aperture, which is preferablebecause a mechanism is simple.

[0253] (11-29)

[0254] However, it is also possible to use a filter such as a hologramfilter to generate flare. Incidentally, when providing a filter such asa hologram filter, a separated filter may be provided in the opticalconverging system, or a filter may be provided on the objective lens.

[0255] It is possible either to provide flare to be under for theposition to make the minimum spot when the light flux located where theprescribed numerical aperture is more smaller are converged, or toprovide flare to be over. The preferable is to provide to be over.

[0256] When generating flare as stated above, it is possible to generateflare continuously on the spherical aberration diagram or to generateflare discontinuously.

[0257] Further, an another embodiment, there is given an embodiment ofan optical pickup apparatus wherein no flare is generated. The followingone is given.

[0258] (11-30)

[0259] In other words, it is possible to express as follows. The firstlight flux which is within a prescribed numerical aperture, of a firstoptical information recoding medium, of the objective lens on the imageside in the case of using the first light flux is converged on a firstinformation recording plane of a first optical information recordingmedium under the state of 0.07 λrms or less, and the first light fluxwhich has passed the outside of a prescribed numerical aperture of theobjective lens on the image side in the case of using the first lightflux is converged on the first information recording plane under thestate of 0.07 λrms or less, or it is blocked and does not reach thefirst information recording plane. The second light flux which haspassed the inside of a prescribed numerical aperture of the objectivelens on the image side in the case of using the first light flux, andthe second light flux which has passed the outside of a prescribednumerical aperture are converged on a second information recording planeof a second optical information recording medium under the state of 0.07λrms or less. In this case, NA1 is smaller than NA2, and a light fluxbetween NA1 and NA2 is also converged or blocked, when conductingrecording or reproducing for the first optical information recordingmedium.

[0260] (11-31)

[0261] Or, the second light flux which is within a prescribed numericalaperture, of a second optical information recoding medium, of theobjective lens on the image side in the case of using the second lightflux is converged on a second information recording plane of a secondoptical information recording medium under the state of 0.07 λrms orless, and the second light flux which has passed the outside of aprescribed numerical aperture of the objective lens on the image side inthe case of using the second light flux is converged on the secondinformation recording plane under the state of 0.07 λrms or less, or itis blocked and does not reach the second information recording plane.The first light flux which has passed the inside of a prescribednumerical aperture of the objective lens on the image side in the caseof using the second light flux, and the first light flux which haspassed the outside of a prescribed numerical aperture are converged on afirst information recording plane of a first optical informationrecording medium under the state of 0.07 λrms or less. In this case, NA1is greater than NA2, and a light flux between NA2 and NA1 is alsoconverged or blocked, when conducting recording or reproducing for thesecond optical information recording medium.

[0262] These embodiments can be established voluntarily by the design ofthe diffractive portion.

[0263] (11-32)

[0264] In the embodiment wherein the flare is not generated and a lightflux between NA1 and NA2 or between NA2 and NA1 is blocked, it ispreferable to provide an aperture regulating means which blocks thefirst light flux which is outside a prescribed numerical aperture of theobjective lens on the image side in the case of using the first lightflux and transmits the second light flux, or an aperture regulatingmeans which blocks the second light flux which is outside a prescribednumerical aperture of the objective lens on the image side in the caseof using the second light flux and transmits the first light flux. Or,it is preferable to provide an aperture regulating means wherein eachlight flux has its own prescribed numerical aperture.

[0265] (11-33)

[0266] Namely, it is preferable that a light flux is blocked by aring-zonal filter such as a dichroic filter or a hologram filterrepresenting an aperture regulating means at the prescribed numericalaperture or more for either one of the first light flux or the secondlight flux. Incidentally, when providing a dichroic filter or a hologramfilter, a separate filter may be provided in an optical convergingsystem, or a filter may be provided on an objective lens.

[0267] (11-34)

[0268] However, even when no flare is generated, it is also possible tomake all light fluxes within the maximum numerical aperture to beconverged on an information recording plane by providing only anordinary aperture without providing a dichroic filter or a hologramfilter. In other words, it is also possible to make the first light fluxand the second light flux within the maximum numerical aperture of theobjective lens on the image side to be converged on an informationrecording plane under the state of 0.07 λrms. It may be preferable thatno flare is generated by the above embodiment when NA1=NA2.

[0269] (11-35)

[0270] Incidentally, the first optical information recording medium andthe second optical information recording medium both representingdifferent information recording media mean information recording mediaeach having a different wavelength of light used for eachrecording/reproducing. A thickness and a refractive index of atransparent substrate may either be the same or be different. Aprescribed numerical aperture may either be the same or be different. Aprescribed numerical aperture may either be the same or be different,and the recording density for information also may be the same or bedifferent.

[0271] Paraxial chromatic aberration and spherical aberration caused bya difference of a wavelength of light used for recording/reproducing ofeach of different information recording media are corrected by thediffractive portion of the invention. Incidentally, it is mostpreferable that both spherical aberration and paraxial chromaticaberration are corrected, and an embodiment wherein spherical aberrationonly is corrected and paraxial chromatic aberration is not corrected ispreferable next, while, an embodiment wherein paraxial chromaticaberration only is corrected and spherical aberration is not correctedis also acceptable. Incidentally, as a concrete embodiment of theoptical information recording medium, CD, CD-R, CD-RW, DVD, DVD-RAM, LD,MD, MO and so on may be listed. However, it may be not limited to these.Further, an optical information recording medium employing blue lasermay be used.

[0272] (11-36)

[0273] Even in the case where a thickness of a transparent substrate isdifferent in different information recording media, and sphericalaberration is caused based on the thickness of the transparentsubstrate, the spherical aberration is corrected by the diffractiveportion of the invention. Incidentally, when a thickness of atransparent substrate is different in a first optical informationrecording medium and a second optical information recording medium, alevel of the caused spherical aberration is higher, and therefore, theeffect of the invention is more remarkable, which is preferable.

[0274] (11-37)

[0275] Incidentally, it is preferable that a difference between thewavelength of the first light flux and the wavelength of the secondlight flux is in a range from 80 nm to 400 nm. The more preferable is ina range from 100 nm to 200 nm. Further preferable is in a range from 120nm to 200 nm. As the first light source and the second light source, itis possible to select two types of light sources from those emittinglight of wavelengths 760-820 nm, 630-670 nm and 350-480 nm, for example,to combine them for use. Three light sources or four light sources arenaturally acceptable. When the third light source emitting the thirdlight flux and the fourth light source emitting the fourth light fluxare provided, it is preferable that n-th ordered diffracted ray isgenerated more than other ordered diffracted ray even in the third lightflux and the fourth light flux which have passed the diffractiveportion.

[0276] (11-38)

[0277] When the wavelength of the second light flux is longer than thewavelength of the first light flux, it is preferable that paraxialchromatic aberration in the second light flux and that in the firstlight flux satisfy the following conditional expression.

−λ₂/(2NA ₂ ²)≦Z≦λ ₂/(2NA ₂ ²)

[0278] λ₂: Wavelength of the second light flux

[0279] NA₂: Prescribed numerical aperture, of the second opticalinformation recording medium, of the objective lens on the image sidefor the second light flux

[0280] (11-39)

[0281] When a recording medium having a different thickness of atransparent substrate is used, it is preferable that the followingexpression is satisfied in the case of t2>t1 and λ2>λ1.

0.2×10⁻⁶ /° C.<ΔWSA3·λ1/{f·(NA1)⁴ ·ΔT}<2.2×10⁻⁶ /° C.

[0282] NA1: Prescribed numerical aperture, of the first opticalinformation recording medium, of the objective lens on the image sidefor the use of the first light flux

[0283] λ1: Wavelength of the first light flux

[0284] f1: Focal length of the objective lens for the first light flux

[0285] ΔT: Ambient temperature fluctuation

[0286] ΔWSA3 (λ 1rms): An amount of fluctuation of 3-ordered sphericalaberration component of spherical aberration of a light flux convergedon an optical information recording plane in the case of reproducing orrecording the optical information recording medium by the use of thefirst light flux

[0287] (11-40)

[0288] It is also possible to arrange so that the first light fluxrepresenting a non-collimated light flux such as diverged light orconverged light is made to enter the objective lens in the case of usingthe first light flux, and the second light flux representing anon-collimated light flux such as diverged light or converged light ismade to enter the objective lens in the case of using the second lightflux.

[0289] (11-41)

[0290] Or, the first light flux representing a collimated light flux maybe made to enter the objective lens in the case of using the first lightflux, and the second light flux representing a non-collimated light fluxsuch as diverged light or converged light may also be made to enter theobjective lens in the case of using the second light flux. Or, it isalso possible to arrange so that the first light flux representing anon-collimated light flux such as diverged light or converged light ismade to enter the objective lens in the case of using the first lightflux, and the second light flux representing a collimated light is madeto enter the objective lens in the case of using the second light flux.

[0291] When using a non-collimated light flux in either of the firstlight flux and the second light flux, or in both light fluxes of them,it is preferable that an absolute value of a difference betweenmagnification m1 of an objective lens in using the first light flux andmagnification m2 of an objective lens in using the second light flux isin a range of 0-{fraction (1/15)}. The more preferable range is0-{fraction (1/18)}. In the case of λ2>λ1 and t2>t1, it is preferablethat m1 is greater. In particular, when using the second light flux andthe first light flux respectively for CD and DVD, the aforesaid range ispreferable. Incidentally, a wavelength of the first light source isrepresented by λ1, a wavelength of the second light source isrepresented by λ2, a thickness of the first transparent substrate isrepresented by t1 and a thickness of the second transparent substrate isrepresented by t2.

[0292] Or, it is also possible to arrange so that the first light fluxrepresenting a collimated light flux and the second light fluxrepresenting a collimated light flux may also be made to enter theobjective lens. In this case, it is preferable that the diffractiveportion is in the form shown in FIGS. 47(a) and 47(b), although it mayalso be in the form shown in FIGS. 47(b) and 47(c).

[0293] (11-42)

[0294] Further, it is also possible to provide, on an optical pickupapparatus, a divergence changing means which changes divergence of alight flux entering an objective lens, and thereby to change divergenceof a light flux entering an objective lens in the first light flux andthe second light flux.

[0295] Incidentally, when a diverged light enters an objective lens, itis preferable that the objective lens is a glass lens.

[0296] Incidentally, when reproducing and recording can be conductedonly for either one of the first information recording medium and thesecond information recording medium, and reproducing only is conductedfor the other one of them, it is preferable that an image formingmagnification of the total optical pickup apparatus for the first lightflux is different from an image forming magnification of the totaloptical pickup apparatus for the second light flux, in the opticalpickup apparatus. In this case, an image forming magnification of theobjective lens for the first light flux may either be equal to or bedifferent from an image forming magnification of the objective lens forthe second light flux.

[0297] Further, when reproducing and recording can be conducted only forthe first information recording medium, and reproducing only isconducted for the second information recording medium in the case ofλ1<λ2 and t1<t2, it is preferable that the image forming magnificationof the total optical pickup apparatus for the first light flux issmaller than that of the total optical pickup apparatus for the secondlight flux. Further, when the foregoing is satisfied in the case of0.61<NA1<0.66, it is preferable that a coupling lens which changes amagnification is provided between the first light source and acollimator lens in the optical converging system, and a collimator lensfor the first light flux and a collimator lens for the second light fluxare provided separately in the optical converging system. Incidentally,it is preferable that both of the image forming magnification of theobjective lens for the first light flux and the image formingmagnification of the objective lens for the second light flux are zero.Incidentally, a wavelength of the first light source is represented byλ1, a wavelength of the second light source is represented by λ2, athickness of the first transparent substrate is represented by t1, athickness of the second transparent substrate is represented by t2, anda prescribed numerical aperture of the objective lens which is necessaryfor recording or reproducing of the first optical information recordingmedium on the image side is represented by NA1.

[0298] Further, when reproducing and recording can be conducted only forthe second information recording medium, and reproducing only isconducted for the first information recording medium in the case ofλ1<λ2 and t1<t2, it is preferable that the image forming magnificationof the total optical pickup apparatus for the first light flux isgreater than that of the total optical pickup apparatus for the secondlight flux. Incidentally, it is preferable that both of the imageforming magnification of the objective lens for the first light flux andthe image forming magnification of the objective lens for the secondlight flux are zero.

[0299] Incidentally, when reproducing and recording can be conducted forboth the first information recording medium and the second informationrecording medium, or when reproducing only is conducted for both ofthem, it is preferable that an image forming magnification of the totaloptical pickup apparatus for the first light flux is the almost samewith an image forming magnification of the total optical pickupapparatus for the second light flux, in the optical pickup apparatus. Inthis case, an image forming magnification of the objective lens for thefirst light flux may either be equal to or be different from an imageforming magnification of the objective lens for the second light flux.

[0300] (11-43)

[0301] Further, the photo detector may be made to be common for both thefirst light flux and the second light flux. Or, it is also possible toprovide a second photo detector so that the photo detector is made to befor the first light flux, and the second photo detector is made to befor the second light flux.

[0302] (11-44)

[0303] The photo detector and the first light source or the photodetector and the second light flux may be unitized. Or, the photodetector, the first light source and the second light source may beunitized. Or, the photo detector, the second photo detector, the firstlight source and the second light source may all be unitized integrally.Further, the first light source and second light source only may beunitized.

[0304] In particular, when the first light source and the second lightsource are unitized respectively and are arranged side by side on thesame plane, it is preferable to provide the first light source on theoptical axis of the objective lens in the case of NA1 >NA2, and it ispreferable to provide the second light source on the optical axis of theobjective lens in the case of NA1 <NA2. Incidentally, a prescribednumerical aperture of the objective lens which is necessary forrecording or reproducing of the first optical information recordingmedium on the image side is represented by NA1, and a prescribednumerical aperture of the objective lens which is necessary forrecording or reproducing of the second optical information recordingmedium on the image side is represented by NA2.

[0305] Incidentally, when WD1 represents a working distance in recordingand reproducing the first optical information recording medium and WD2represents a working distance in recording and reproducing the secondoptical information recording medium, |WD1−WD2|≦0.29 mm is preferable.In this case, it is preferable that a magnification for recording andreproducing of the first optical information recording medium is thesame as that for recording and reproducing of the second opticalinformation recording medium. The more preferable is that themagnification is zero. Further, in the case of t1<t2 and λ1<λ2, WD1≧WD2is preferable. These conditions about a working distance are especiallypreferable when the first optical information recording medium is DVDAND the second optical information recording medium is CD. Incidentally,when the aforesaid working distance is satisfied, the form of thediffractive portion shown in FIGS. 47(b) and 47(c) is more preferablethan that shown in FIGS. 47(a) and 47(d).

[0306] Further, the converging optical system or the optical elementsuch as an objective lens forms a spot so that a light flux may beconverged on an information recording plane of an optical informationrecording medium for recording and reproducing of information. Inparticular, when NA1 is greater than NA2 and λ1 is smaller than λ2, anda light flux outside NA2 is made to be flare (wave-front aberration onan image forming plane is made to be greater than 0.07 λ2rms) on thesecond information recording plane of the second optical informationrecording medium, concerning the second light flux, it is preferablethat the spot satisfies the following conditions.

0.66 λ2/NA2≦w≦1.15 λ2/NA2

w>0.83 λ2/NA1

[0307] λ1: Wavelength of first light flux

[0308] λ2: Wavelength of second light flux

[0309] NA1: Prescribed numerical aperture of a first optical informationrecording medium for first light flux

[0310] NA2: Prescribed numerical aperture of a second opticalinformation recording medium for second light flux

[0311] w: Beam diameter of 13.5% intensity of second light flux on imageforming plane

[0312] Incidentally, when the spot is not a complete round, it ispreferable that the beam diameter in the direction where the beamdiameter is converged most is made to be the aforesaid beam diameter(w).

[0313] It is more preferable that the following conditions aresatisfied.

0.74 λ2/NA2≦w≦0.98 λ2/NA2

[0314] With regard to a form of the spot, it may either be one wherein aspot of high light intensity used for recording and reproducing islocated at the center, and flare which is low in terms of lightintensity to the degree not to affect the detection adversely is locatedcontinuously around the spot, or be one wherein a spot of high lightintensity used for recording and reproducing is located at the center,and flare is located around the spot in the form of a doughnut.

[0315] (11-45)

[0316] Further, in order to detect information very well, it may bepreferable that S-shaped characteristic is good. More concretely, it maybe preferable that over shoot is 0% to 20%.

[0317] When λ1 represents a wavelength of the first light source, λ2represents a wavelength of the second light source, t1 represents athickness of the first transparent substrate, t2 represents a thicknessof the second transparent substrate, NA1 represents a prescribednumerical aperture of an objective lens on the image side which isneeded for recording or reproducing the first optical informationrecording medium by first light flux, and NA2 represents a prescribednumerical aperture of an objective lens on the image side which isneeded for recording or reproducing the second optical informationrecording medium by second light flux, there is given the followingconditional expression as a preferable example. In this case, it ispreferable that n-th ordered diffracted ray is positive first ordereddiffracted ray. A preferable embodiment is not naturally limited to thefollowing conditional expression.

λ1<λ2

t1<t2

NA1>NA2 (preferably, NA1>NA2>0.5×NA1)

[0318] In the case that the above conditional formula is satisfied, theobjective lens of the converging optical system comprises a diffractiveportion, and in the case that the converging optical system convergesthe n-th ordered diffracted ray in the second light flux having passedover the diffractive portion on the second information recording planeof the second information recording medium, the spherical aberration maycomprises a discontinuing section in at least one place as shown in FIG.112.

[0319] In case of comprising the discontinuing section, at a place nearNA2, it may be preferable that the spherical aberration may comprises adiscontinuing section. For example, following case may be listed. At aplace where NA=0.45, the spherical aberration comprises a discontinuingsection, and at a place where NA=0.5, the spherical aberration comprisesa discontinuing section.

[0320] In case that the spherical aberration comprises a discontinuingsection, the converging optical system converges the n-th ordereddiffracted ray having a numerical aperture smaller than NA1 in the firstlight flux having passed over the diffractive portion on the firstinformation recording plane of the first recording medium such that thewave-front aberration at the best image point is 0.07 λrms and theconverging optical system converges the n-th ordered diffracted rayhaving a numerical aperture smaller than that of the discontinuingsection in the second light flux having passed over the diffractiveportion on the second information recording plane of the secondrecording medium such that the wave-front aberration at the best imagepoint is 0.07 λrms.

[0321] Further, in the case that the above conditional formula issatisfied, it may be that the conversion optical system comprises anobjective lens, and the objective lens has a diffractive portion, incase that the converging optical system converges the n-th ordereddiffracted ray of the second light flux having passed over thediffractive portion on the second information recording plane of thesecond optical information recording medium in order to conduct therecording or the reproducing for the second optical informationrecording medium, the spherical aberration is continued without having adiscontinuing section as shown in FIG. 27.

[0322] In the case that the spherical aberration is continued withouthaving a discontinuing section, it may be preferable that the sphericalaberration at NA1 is not smaller than 20 μm and the spherical aberrationat NA2 is not larger than 10 μm. It may be more preferable tht thespherical aberration at NA1 is not smaller than 50 μm and the sphericalaberration at NA2 is not larger than 2 μm.

[0323] (11-46)

[0324] There is given the following embodiment as a concrete andpreferable example wherein one type of DVD is used as a first opticalinformation recording medium and one type of CD is used as a secondoptical information recording medium in the aforesaid condition, towhich the invention is not limited.

0.55 mm<t1<0.65 mm

1.1 mm<t2<1.3 mm

630 nm<λ1<670 nm

760 nm<λ2<820 nm

0.55<NA1<0.68

0.40<NA2<0.55

[0325] When the diffractive portion is ring-zonal diffraction in thecase of the aforesaid range, it is preferable that the diffractionportion corresponding to NA2 or less is not more than 19 annular bandsor not less than 21 annular bands. It is also preferable that the totaldiffraction portion is not less than 35 annular bands or not more than33 annular bands.

[0326] (11-47)

[0327] Further, in the case that the above range is satisfied, it may bepreferable that the diameter of spot satisfy the following embodiment.The conversion optical system comprises an objective lens, the objectivelens has a diffractive portion, λ1=650 nm, t1=0.6 mm, and NA1=0.6, andwherein in case that the first light flux which is composed of parallelrays and have a uniform intensity distribution are introduced in theobjective lens and are converged on the first information recordingplane through the first transparent substrate, a diameter of convergedspot is 0.88 μm to 0.91 μm at the best focusing condition.

[0328] Further, it may be preferable that λ1=650 nm, t1=0.6 mm, andNA1=0.65 and wherein in case that the first light flux which is composedof parallel rays and have a uniform intensity distribution areintroduced in the objective lens and are converged on the firstinformation recording plane through the first transparent substrate, adiameter of converged spot is 0.81 μm to 0.84 μm at the best focusingcondition.

[0329] Furthermore, in the case that the above range is satisfied andthe diffractive portion is provided on an objective lens, a pitch of thediffractive portion at NA=0.4 is 10 μm to 70 μm. It may be morepreferable that the pitch is 20 μm to 50 μm.

[0330] Further, there is given the following embodiment as a concreteand preferable example in the aforesaid condition, but the invention isnot limited to this. When conducting also recording for CD as a secondoptical information recording medium, in particular, it is preferablethat NA2 is 0.5. Further, when conducting recording also for the firstoptical information recording medium as DVD, NA1 which is 0.65 ispreferable.

t1=0.6 mm

t2=1.2 mm

λ1=650 nm

λ2=780 nm

NA1=0.6

NA2=0.45

[0331] (11-48)

[0332] The following embodiment is also acceptable. In the case of thefollowing embodiment, it is preferable that n-th ordered diffracted rayis negative first ordered light.

λ1<λ2

t1>t2

[0333] (11-49)

[0334] As a concrete example of an optical information recording mediumreproducing or recording apparatus for reproducing information from anoptical information recording medium or for recording information ontothe optical information recording medium, having an optical pickupapparatus of the invention, there are given a DVD/CD reproducingapparatus, a DVD/CD/CD-R recording and reproducing apparatus, aDVD-RAM/DVD/CD-R/CD recording and reproducing apparatus, a DVD/CD/CD-RWrecording and reproducing apparatus, a DVD/LD reproducing apparatus,DVD/ an optical information recording medium recording and reproducingapparatus employing blue laser, CD/ and an optical information recordingmedium recording and reproducing apparatus employing blue laser, towhich the invention is not limited. These optical information recordingmedium reproducing or recording apparatuses have a power supply and aspindle motor in addition to the optical pickup apparatus.

[0335] Next, a preferable embodiment of the present invention will beexplained.

[0336] In ordered to attain the above object, an optical system of Item1 includes more than 1 optical element, and in the optical system usedfor at least either one of recording or reproducing of the informationonto or from an information recording medium, at least one of theoptical elements has a diffraction surface which selectively generatesthe same ordered diffracted ray for the light of at least 2 wavelengthswhich are different from each other.

[0337] According to Item 1, because the optical element has thediffraction surface, the spherical aberration can be corrected for thelight of at least 2 wavelengths which are different from each other, andthe axial chromatic aberration can also be corrected. That is, by asimple structure in which many optical elements such as the objectivelens, or similar lenses, are used in common with each other, thespherical aberration and the axial chromatic aberration can becorrected, thereby, the size and weight of the optical system can bereduced, and the cost can be reduced. Further, because the opticalsystem has a diffraction surface which selectively generates the sameordered diffracted ray for the light of at least 2 wavelengths which aredifferent from each other, the loss of the light amount can be reduced,and even when the necessary numerical apertures are different, forexample, by using the common objective lens, a sufficient light amountcan be obtained.

[0338] Further, in the optical system of Item 2, in an optical system inwhich more than 1 optical element is included and which is used for atleast one of recording and reproducing of the information onto or fromthe information recording medium, the diffraction surface whichselectively generates respectively a specific ordered of the diffractedray for the light having at lest 2 wavelengths which are different fromeach other is formed on almost entire surface of at least one opticalsurface of at least one optical element of the above-described opticalelements.

[0339] According to Item 2, because the diffraction surface is formed onthe optical element, in the same manner as Item 1, the sphericalaberration and the axial chromatic aberration can be corrected for thelight having at lest 2 wavelengths which are different from each other.Further, because the diffraction surface is formed on almost entiresurface of at least one optical surface of the optical element, thecorrection can be more effectively carried out.

[0340] Incidentally, each term is defined as follows. Initially, anoptical element indicates each of all optical elements applicable to theoptical system to record the information onto the information recordingmedium and/or to reproduce the information on the information recordingmedium, and generally, a coupling lens, objective lens, polarizing beamsplitter, ¼ wavelength plate, or beam splitter to synthesize the lightfrom more than 2 light sources, or the like, are listed, however, theoptical element is not limited to these. Further, the optical elementwhich is provided with only the diffractive portion of the presentinvention and has not the other function, may be used.

[0341] Further, an optical system in the present invention is more than1 assemblage of the optical elements to enable recording of theinformation onto or reproducing of the information on, for example, theCD and DVD, and may mean not only the whole optical system to enablerecording of the information onto the information recording mediumand/or reproducing of the information on the information recordingmedium, but also may means a portion of the optical system, and anoptical system includes at least 1 optical element as described above.

[0342] As the information recording medium in the present invention, thedisk-like information recording media, for example, each kind of CD suchas the CD, CD-R, CD-RW, CD-Video, CD-ROM, etc., or each kind of DVD suchas the DVD, DVD-ROM, DVD-RAM, DVD-R, DVD-RW, etc., or the MD, LD, MO orthe like, are listed. Generally, a transparent substrate exists on theinformation recording surface of the information recording medium.Needless to say, the information recording media is not limited theabove. The information recording media used in the present inventioncomprises an optical information recording media such as a blue laseravailable in a current market.

[0343] In the present invention, recording of the information onto theinformation recording medium, or reproducing of the information on theinformation recording medium mean to record the information onto theinformation recording surface of the information recording medium, andto reproducing the information recorded on the information recordingsurface. The pickup apparatus and the optical system in the presentinvention may a pickup apparatus and be an optical system used for onlyrecording, or only reproducing, and may also be a pickup apparatus andan optical system used for both of recording and reproducing. Further,the pickup apparatus and the optical system may be used for recordingonto one information recording medium and for reproducing from anotherinformation recording medium, or for recording and reproducing for oneinformation recording medium, and for recording and reproducing foranother information recording medium. Incidentally, the reproducing usedherein includes only reading-out of the information.

[0344] Further, the pickup apparatus and the optical system used for atleast either one of recording or reproducing for the informationrecording medium includes a pickup apparatus and an optical system, ofcourse, applicable for the above purpose, and also a pickup apparatusand an optical system which is actually used, or intended to be used forsuch the purpose.

[0345] In the present invention, the light having at least 2 wavelengthswhich are different from each other, may be the light having 2 differentwavelengths, for example, the light having 780 nm wavelength used forthe CD, and 635 nm or 650 nm wavelength used for the DVD, and may be thelight having 3 different wavelengths, which further includes, forexample, the light having 400 nm wavelength for recording and/orreproducing of the large capacity information recording medium which isdensification-recorded. Of course, the light having more than 4different wavelengths may be allowable. Further, even in the opticalsystem in which, actually, more than 3 different wavelengths are used,or the optical system in which that is intended, of course, it means thelight having at least 2 different wavelengths in them. As a matter ofcourse, a combination of 400 nm and 780 nm or a combination of 400 nmand 650 nm may be used.

[0346] In the present invention, the light having different wavelengthmeans the light having a plurality of wavelengths with a sufficientdifference of wavelength from each other, which is used corresponding tokinds of the information recording medium, as described above, or thedifference of the recording density, however, it does not means thelight having the wavelength which differs due to the temporary shiftwithin about ±10 nm caused by the temperature change or output change of1 light source which outputs the light having 1 wavelength. Further, asfactors that the light having different wavelengths is used, other thanthe above-described kinds of the information recording media or thedifference of recording density, for example, the difference of thethickness of the transparent substrate of the information recordingmedium, or the difference between recording and reproducing, is listed.

[0347] Further, the diffraction surface means the surface in which arelief is provided on the surface of the optical element, for example,on the surface of the lens, and which has the function to converge ordiverge the flux of light by the diffraction, and when there is an areain which the diffraction occurs, and an area in which the diffractiondoes not occur on the same optical surface, it means the area in whichthe diffraction occurs. As the shape of the relief, for example, aconcentric ring band is formed around the optical axis on the surface ofthe optical element, and when the cross section is viewed on the planeincluding the optical axis, it is known that each ringband,(hereinafter, the ring band is called the annular band), has thesaw tooth-like shape, and the diffraction surface includes such theshape.

[0348] Generally, from the diffraction surface, the infinite ordereddiffracted ray, such as zero ordered light, ±first ordered light,±second ordered light, . . . , is generated, and in the case of thediffraction surface in which the meridian cross section has thesaw-toothed relief as described above, the shape of the relief can beset so that the diffraction efficiency of the specific ordered is madehigher than that of the other ordered, or in a certain circumstance, thediffraction efficiency of a specific one ordered (for example, +firstordered light) is made almost 100%. In the present invention, thediffracted ray of the specific ordered is selectively generated, meansthat, to the light having a predetermined wavelength, the diffractionefficiency of the diffracted ray of the specific ordered is higher thanthat of respective diffracted ray of the other ordered except thespecific ordered, and to the respective light having 2 wavelength whichare different from each other, the specific ordered of the specificordered diffracted ray which is respectively selectively generated, isthe same ordered, means that the same ordered diffracted ray isselectively generated. Herein, the ordered of the diffracted ray is thesame, means that the ordered of the diffracted ray is the same includingits sign.

[0349] Further, the diffraction efficiency is obtained such that therate of the light amount of the diffracted ray of respective ordereds tothe all diffracted ray is obtained according to the shape of thediffraction surface (the shape of the relief), and obtained by acalculation by the simulation in which the wavelength of the light to beirradiated is set to a predetermined wavelength. As the predeterminedwavelength, as an example, the wavelength of 780 nm, or 650 nm islisted.

[0350] Further, the diffraction surface is formed on almost entiresurface of at least one optical surface of the optical element, meansthat the diffraction structure (relief) is provided on at least almostall of the range through which the light flux passes on the opticalsurface, and that it is not the optical element in which the diffractionstructure is provided on a portion of the optical surface, for example,the diffraction structure is provided, for example, on only theperipheral portion. In this case, the range through which the light fluxfrom the light source passes to the information recording medium side,is determined by the aperture diaphragm used for the optical system orthe optical pickup apparatus. The range in which the diffraction surfaceis formed, ranges over almost all surface of the optical surface when itis viewed as the optical element single body provided with thediffraction surface, however, generally, the optical surface is formedalso on the peripheral portion through which the light flux does notpass, with a certain degree of the margin, therefore, when this portionis considered being included in the optical surface as an available areaas the optical surface, it is preferable that the ratio of the area ofthe diffraction surface in the optical surface is at least more thanhalf as the optical element single body, and more preferably it isalmost 100%.

[0351] Further, the optical system in Item 3 is characterized in thatthe specific ordered of the diffracted ray respectively generatedselectively is the same ordered to the respective light having 2wavelengths which are different from each other.

[0352] According to Item 3, because the diffraction surface makes thediffraction efficiency of the diffracted ray of the same ordered,maximum to the respective light having at least 2 wavelengths, the lossof the light amount is smaller as compared to the case in which thediffraction surface makes the diffraction efficiency of the diffractedray of the different ordered, maximum.

[0353] Further, the optical system in Item 4 is characterized in thatthe same ordered diffracted ray is the first ordered diffracted ray. Thefirst ordered diffracted ray may be +first ordered diffracted ray, or−first ordered diffracted ray.

[0354] According to Item 4, because the same ordered diffracted ray isthe first ordered diffracted ray, the loss of the light amount issmaller as compared to the case in which the same ordered diffracted rayis the higher ordered diffracted ray than the first ordered diffractedray.

[0355] Further, the optical system in Item 5 is characterized in that atleast 1 optical element of the optical element having the diffractionsurface is a lens having the refraction power. The optical system inItem 5 may be the optical system in which a fine structure (relief) forthe diffraction is further formed on the surface of the lens having therefraction power. In this case, the enveloping surface of the finestructure for diffraction is the shape of diffraction surface of thelens. For example, so called blaze type diffraction surface is providedon at least one surface of the aspherical single lens objective lens,and it may be a lens, on the entire surface of which the annular bandwhose meridian cross section is the saw-toothed shape is provided.

[0356] According to Item 5, because the optical element having thediffraction surface is the lens having the refraction power, both of thespherical aberration and the chromatic aberration can be corrected, andthe number of parts can be reduced.

[0357] Further, the optical system in Item 6 is characterized in thatthe shape of the diffraction surface of the lens is aspherical.

[0358] Further, the optical system in Item 7 is characterized in thatthe lens makes the diffraction efficiency of the diffracted ray for thelight having a certain 1 wavelength which is the wavelength between themaximum wavelength and the minimum wavelength of the at least 2wavelengths which are different from each other, larger than thediffraction efficiency of the diffracted ray for the light having themaximum wavelength and the minimum wavelength.

[0359] Further, the optical system in Item 8 is characterized in thatthe lens makes the diffraction efficiency of the diffracted ray for thelight having the maximum wavelength and the minimum wavelength of the atleast 2 wavelengths which are different from each other, larger than thediffraction efficiency of the diffracted ray for the light having thewavelength which is the wavelength between the maximum wavelength andthe minimum wavelength of the at least 2 wavelengths which are differentfrom each other.

[0360] Further, the optical system in Item 9 is characterized in thatthe positive and negative signs of the diffraction effect which is addedby the diffraction surface of the lens are switched at least one time inthe direction separating from the optical axis perpendicularly to theoptical axis.

[0361] According to Item 9, because the positive and negative signs ofthe diffraction effect which is added by the diffraction surface of thelens are switched at least one time in the direction separating from theoptical axis perpendicularly to the optical axis, thereby, the variationof the wavelength of the spherical aberration can be suppressed.

[0362] Further, the optical system in Item 10 is characterized in thatthe diffraction effect which is added by the diffraction surface of thelens are switched one time from the negative to the positive in thedirection separating from the optical axis perpendicularly to theoptical axis.

[0363] According to Item 10, because the diffraction power which isadded by the diffraction surface of the lens is switched one time fromthe negative to the positive in the direction separating from theoptical axis perpendicularly to the optical axis, thereby, when, forexample, the parallel light flux enters into the objective lens in theCD system and the DVD system, the influence on the spherical aberrationdue to the difference of the thickness of the transparent substrate ofthe information recording medium can be effectively corrected withoutmaking the annular band pitch of the diffraction surface too small.

[0364] Relating to the diffraction power, particularly, in the case ofthe optical element provided with the optical surface having therefraction action and the diffraction action, in other words, in thecase of the optical element in which the diffraction surface is providedon the optical surface having the refraction action, by the action ofthe diffraction surface, the action to converge or diverge the lightflux is added to the refraction action of the refraction surface whichis the base. In this case, when converging action is added to the lightray which is in actual finite height, not limited to the paraxial area,in the present invention, the following is defined: a predeterminedposition of the refraction surface has the positive diffraction power,and when the diverging action is added, it has the negative power.

[0365] The optical system in Item 11 is characterized in that thediffraction surface is formed of a plurality of annular bands viewedfrom the optical axis, and the plurality of annular bands are formedinto almost concentric circle-like one around the optical axis or apoint near the optical axis. That is, the diffraction surface of Item 11is, for example, as disclosed in Japanese Tokkaihei No. 6-242373, formedstepwise as the annular band, which shifts discretely in the directionin which the lens thickness is increased as being separated from theoptical axis.

[0366] Further, the optical system in Item 12 is characterized in thatthe phase difference function expressed by the power series showing eachposition of the plurality of annular bands has a factor except zero inat least 1 term except the 2nd power term.

[0367] According to Item 12, the spherical aberration can be controlledbetween 2 different wavelengths. Herein, “can be controlled” means thatthe difference of the spherical aberration can be made very smallbetween 2 wavelengths, and the difference necessary for the opticalspecification can be provided.

[0368] Further, the optical system in Item 13 is characterized in thatthe phase difference function expressed by the power series showing eachposition of the plurality of annular bands has a factor except zero in2nd power term.

[0369] According to Item 14, the correction of the chromatic aberrationin the paraxial area can be effectively conducted.

[0370] Further, the optical system in Item 13 is characterized in thatthe phase difference function expressed by the power series showing eachposition of the plurality of annular bands does not include the 2ndpower term.

[0371] According to Item 14, because the phase difference function doesnot include the 2nd power term, the paraxial power of the diffractionsurface becomes 0, and only the term more than 4th power is used,thereby, the pitch of the diffraction annular band is not too small, andthe spherical aberration can be controlled.

[0372] The optical system in Item 15 is characterized in that theobjective lens is included in the more than 1 optical element, and toeach of the light having at least 2 wavelengths (wavelength λ) which aredifferent from each other, the wave front aberration on the imageformation surface is not more than 0.07 λrms in a predeterminednumerical aperture on the image side of the objective lens.

[0373] According to Item 15, because the wave front aberration is notmore than 0.07 λrms, which is Mareshall's allowable value, in apredetermined numerical aperture on the image side of the objectivelens, thereby, an excellent optical characteristic in which thespherical aberration is fully small, can be obtained.

[0374] The optical system in Item 16 is characterized in that, even ifone wavelength λ₁ of at least 2 wavelengths which are different fromeach other, varies within the range of ±10 nm, the wave front aberrationon the image formation surface is not more than 0.07 λ₁rms in thepredetermined numerical aperture on the image side of the objectivelens.

[0375] According to Item 16, even if the wavelength λ₁ varies within therange of ±10 nm, an excellent optical characteristic in which thespherical aberration is fully small, can be obtained.

[0376] Further, the optical system in Item 17 is characterized in thatthe light having the wavelength λ₂ of at least 2 wavelengths which aredifferent from each other, and to the light having the anotherwavelength in which the numerical aperture on the image side of theobjective lens is larger than the predetermined numerical aperture ofthe light having the wavelength λ₂, the wave front aberration on theimage formation surface of the light having the wavelength λ₂ is notsmaller than 0.07 λ₂ rms in the predetermined numerical aperture of thelight having another wavelength.

[0377] According to Item 17, because the wave front aberration of thelight having the wavelength λ₂ is not smaller than 0.07 λ₂rms in thepredetermined numerical aperture (which is not smaller than thepredetermined numerical aperture of the light having the wavelength λ₂)of the light having another wavelength, the appropriate spot diametercan be obtained for the light having the wavelength λ₂. That is, to thenumerical number in the actual use, the aberration is made almost zero,and for the outside portions thereof, the aberration is made into theflare, thereby, the predetermined effects can be obtained.

[0378] Further, the optical system in Item 18 is characterized in thatthe front wave aberration of the light having the wavelength λ₂ on theimage formation surface is not less than 0.10 λ₂rms in the predeterminednumerical aperture of the light having another wavelength.

[0379] According to Item 18, because the front wave aberration of thelight having the wavelength λ₂ is not less than 0.10 λ₂ rms in thepredetermined numerical aperture (which is larger than the predeterminednumerical aperture for the light having the wavelength λ₂) of the lighthaving another wavelength, the more appropriate spot diameter can beobtained for the light having the wavelength λ₂.

[0380] The optical system i Item 19 is characterized in that, when thepredetermined numerical aperture of the light having another wavelengthis NA1, and the predetermined numerical aperture of the light havingwavelength λ₂ is NA2, the optical system satisfies NA1 >NA2>0.5 NA1.

[0381] Further, the optical system in Item 20 is characterized in thatthe parallel light flux for the light having at least 1 wavelength of atleast 2 wavelengths which are different from each other, is entered intothe objective lens, and non-parallel light flux for the light havinganother wavelength, is entered into the objective lens.

[0382] According to Item 20, because the parallel light flux for thelight having at least 1 wavelength of at least 2 wavelengths which aredifferent from each other, is entered into the objective lens, andnon-parallel light flux for the light having at least one otherwavelength, is entered into the objective lens, thereby, to thevariation of about 10 nm of the wavelengths of respective light havingat least 2 wavelengths, the variation of spherical aberration can besuppressed to a very small amount.

[0383] Further, the optical system in Item 21 is characterized in thatthe parallel light flux for the light having at least 2 wavelength of atleast 2 wavelengths which are different from each other, is entered intothe objective lens.

[0384] Further, the optical system in Item 22 is characterized in thatnon-parallel light flux for the light having at least 2 wavelengths, ofat least 2 wavelength which are different from each other, is enteredinto the objective lens.

[0385] Further, the optical system in Item 23 is characterized in that,when the longer wavelength of any 2 wavelengths of at least 2wavelengths which are different from each other is defined as λ₃, andthe predetermined numerical aperture on the image side of the objectivelens for the light having the wavelength λ₃, is defined as NA, the axialchromatic aberration between the wavelength λ₃ and the shorterwavelength is not less than −λ₃/(2NA²) and not more than +λ₃/(2NA²).

[0386] According to Item 23, when the wavelength is switched, becausethe focus is hardly changed, the focus servo is not necessary, and themovement range by the focus servo can be narrowed.

[0387] Further, the optical system in Item 24 is characterized in thatthe light having at least 2 wavelengths which are different from eachother, are respectively used for the information recording media whosetransparent substrate thickness are different from each other.

[0388] Further, the optical system in Item 25 is characterized in thatat least 2 wavelengths which are different from each other, are 3wavelengths which are different from each other.

[0389] Further, the optical system in Item 26 is characterized in that,when 3 wavelengths which are different from each other, are definedrespectively as λ1, λ2, and λ3 (λ1<λ2<λ3), and the predeterminednumerical apertures on the image side of the objective lens for each of3 wavelengths which are different from each other are respectivelydefined as NA1, NA2, and NA3, the following expressions are satisfied:

0.60≦NA1, 0.60≦NA2, 0.40≦NA3≦0.50.

[0390] Further, the optical system in Item 27 is characterized in that afilter which can shield at least one portion of the light entered intothe objective lens at the outside of the smallest predeterminednumerical aperture of the predetermined numerical aperture, is provided.

[0391] Further, the optical systems in Item 28 and Item 29 arecharacterized in that the optical element having the diffraction surfaceis an objective lens.

[0392] Further, the optical system in Item 30 is characterized in thatthe objective lens comprises a piece of lens.

[0393] Further, the optical system in Item 31 is characterized in thatthe diffraction surface is provided on both surfaces of the objectivelens.

[0394] Further, the optical system in Item 32 is characterized in thatAbbe's number νd of the material of the objective lens is not smallerthan 50.

[0395] According to Item 32, when the axial chromatic aberration iscorrected for the light source having 2 different wavelengths, thesecond ordered spectrum can be reduced.

[0396] Further, the optical system in Item 33 is characterized in thatthe objective lens is made of plastics. According to Item 33, theoptical system which is a low cost and light in the weight, can beobtained. Further, the optical system in Item 34 is characterized inthat the objective lens is made of glass. According to Item 33 and Item34, the optical system which is very strong in the temperature change,can be obtained.

[0397] Further, the optical system in Item 35 is characterized in thatthe objective lens has a resin layer in which the diffraction surface isformed, on the surface of the glass lens. According to Item 35, becausethe resin layer in which the diffraction structure can be easily formed,is provided on the glass lens, thereby, the optical system which is verystrong for the temperature change and advantageous in the cost, can beobtained.

[0398] Further, the optical system in Item 36 is characterized in thatthe difference of wavelength between at least 2 wavelengths which aredifferent from each other, is not less than 80 nm.

[0399] Further, the optical system in Item 37 is characterized in thatthe difference of wavelength between at least 2 wavelengths which aredifferent from each other, is not more than 400 nm.

[0400] Further, the optical system in Item 38 is characterized in thatthe difference of wavelength between at least 2 wavelengths which aredifferent from each other, is not less than 100 nm and not more than 200nm.

[0401] Further, the optical system in Item 39 is characterized in that,to each of the light having at least 2 wavelengths which are differentfrom each other, the diffraction efficiency of the specific orderededdiffracted ray which is selectively generated, is higher by more than10% than the diffraction efficiency of respective diffracted ray withthe ordered except the specific ordered.

[0402] Further, the optical system in Item 40 is characterized in that,to each of the light having at least 2 wavelengths which are differentfrom each other, the diffraction efficiency of the specific orderededdiffracted ray which is selectively generated respectively, is higher bymore than 30% than the diffraction efficiency of respective diffractedray with the ordered except the specific ordered.

[0403] Further, the optical system in Item 41 is characterized in that,to each of the light having at least 2 wavelengths which are differentfrom each other, the diffraction efficiency of the specific orderededdiffracted ray which is selectively generated respectively, is more than50%.

[0404] Further, the optical system in Item 42 is characterized in that,to each of the light having at least 2 wavelengths which are differentfrom each other, the diffraction efficiency of the specific orderededdiffracted ray which is selectively generated respectively, is more than70%.

[0405] Further, the optical system in Item 43 is characterized in that,when the specific ordereded diffracted ray which is selectivelygenerated, which has at least 2 wavelengths which are different fromeach other, focuses, because the diffracted surface is provided, thespherical aberration is improved as compared to the case of nodiffraction surface.

[0406] Further, the optical system in Item 44 is characterized in that,to each of the light (wavelength λ) having at least 2 wavelengths whichare different from each other, the wave front aberration on the imageformation surface of the specific ordereded diffracted ray which isselectively generated respectively, is not more than 0.07 λrms.

[0407] Further, the item 45 is a optical pickup apparatus characterizedin that it has above-described each optical system.

[0408] Further, the optical pickup apparatus in Item 46 which comprises:at least 2 light sources which output the light having the wavelengthswhich are different from each other; an optical system including morethan 1 optical element by which the light from the light source isconverged onto the information recording medium; and a light detector todetect the transmitted light from the information recording medium orthe reflected light from the information recording medium, wherein atleast one optical element of the optical elements has the diffractionsurface which selectively generates the same ordereded diffracted ray asthe light having 2 different wavelengths outputted from at least 2 lightsources.

[0409] Further, the optical pickup apparatus in Item 47 which comprises:at least 2 light sources which output the light having the wavelengthswhich are different from each other; an optical system including morethan 1 optical element by which the light from the light source isconverged onto the information recording medium; and a light detector todetect the transmitted light from the information recording medium orthe reflected light from the information recording medium, wherein thediffraction surface which selectively generates respectively specificordereded diffracted ray to respective light having 2 differentwavelengths outputted from at least 2 light sources, is formed on thealmost entire surface of at least one optical surface of at least oneoptical element of the optical elements.

[0410] Further, the optical pickup apparatus in Item 48 is characterizedin that at least one optical element of the optical elements having thediffraction surface described in Item 46 or Item 47 is a lens having thediffraction power.

[0411] Further, the optical pickup apparatus in Item 49 is characterizedin that the lens makes the diffraction efficiency of the diffracted rayto the light having a certain wavelength between the maximum wavelengthor the minimum wavelength of 2 different wavelengths outputted from atleast 2 light sources, larger than the diffraction efficiency of thediffracted ray to the light having the maximum wavelength and theminimum wavelength.

[0412] Further, the optical pickup apparatus in Item 50 is characterizedin that the lens makes the diffraction efficiency of the diffracted rayto the light having the maximum wavelength or the minimum wavelength of2 different wavelengths outputted from at least 2 light sources, largerthan the diffraction efficiency of the diffracted ray to the lighthaving a wavelength between the maximum wavelength and the minimumwavelength of at least 2 different wavelengths which are different fromeach other.

[0413] Further, the optical pickup apparatus in Item 51 is characterizedin that the lens has a flange portion on its outer periphery. Further,the optical pickup apparatus in Item 52 is characterized in that theflange portion has a surface extending in almost vertical direction tothe optical axis of the lens. By this flange portion, the lens can beeasily attached to the optical pickup apparatus, and when a surfaceextending in almost vertical direction to the optical axis is provided,the more accurate attachment can be easily carried out.

[0414] Further, the optical pickup apparatus in Item 53 is characterizedin that the objective lens is included in at least more than 1 opticalelement, and the wave front aberration on the image formation surface toeach of the light (wavelength λ) having 2 different wavelengthsoutputted from at least 2 light sources, is not more than 0.07 λrms inthe predetermined numerical aperture on the image side of the objectivelens.

[0415] Further, the optical pickup apparatus in Item 54 is characterizedin that the objective lens is included in at least more than 1 opticalelement, and the wave front aberration on the image formation surface toeach of the light (wavelength λ) having 2 different wavelengthsoutputted from at least 2 light sources, is not more than 0.07 λrms inthe maximum numerical aperture on the image side of the objective lens.

[0416] Further, the optical pickup apparatus in Item 55 is characterizedin that, even when one wavelength λ₁ of 2 different wavelengthsoutputted from at least 2 light sources, varies within the range of ±10nm, the wave front aberration on the image formation surface is not morethan 0.07 λ₁rms in the predetermined numerical aperture on the imageside of the objective lens.

[0417] Further, the optical pickup apparatus in Item 56 is characterizedin that, to the light having the wavelength λ₂ of 2 differentwavelengths outputted from at least 2 light sources, and the lighthaving another wavelength in which the predetermined numerical apertureon the image side of the objective lens is larger than the predeterminednumerical aperture of the light having the wavelength λ₂, the wave frontaberration on the image formation surface of the light having thewavelength λ₂ is not less than 0.07 λ₂rms in the predetermined numericalaperture of the light having another wavelength.

[0418] Further, the image pick-up apparatus in Item 57 is characterizedin that the wave front aberration on the image formation surface of thelight having the wavelength λ₂ is not less than 0.10 λ₂rms in thepredetermined numerical aperture of the light having another wavelength.

[0419] Further, the image pick-up apparatus in Item 58 is characterizedin that, when the predetermined numerical aperture of the light havinganother wavelength is defined as NA1, and the predetermined numericalaperture of the light having the wavelength λ₂ is defined as NA2, thefollowing expression is satisfied: NA1>NA2>0.5×NA1.

[0420] Further, the image pick-up apparatus in Item 59 is characterizedin that the parallel light flux for the light having at least 1wavelength in 2 different wavelengths outputted from at least 2 lightsources, is entered into the objective lens, and the non-parallel lightflux for the light having at least another wavelength is entered intothe objective lens.

[0421] Further, the image pick-up apparatus in Item 60 is characterizedin that the parallel light flux for the light having 2 differentwavelengths outputted from at least 2 light sources, is entered into theobjective lens.

[0422] Further, the image pick-up apparatus in Item 61 is characterizedin that the non-parallel light flux for the light having 2 differentwavelengths outputted from at least 2 light sources, is entered into theobjective lens.

[0423] Further, the image pick-up apparatus in Item 62 is characterizedin that, when the longer wavelength in 2 different wavelengths outputtedfrom at least 2 light sources is defined as λ₃, and the predeterminednumerical aperture on the image side of the objective lens for the lighthaving the wavelength λ₃ is defined as NA, the axial chromaticaberration between the wavelength λ₃ and the shorter wavelength is notless than −λ₃/(2NA²) and not more than +[₃/(2NA²)

[0424] Further, the image pick-up apparatus in Item 63 is characterizedin that the light having 2 different wavelengths outputted from at least2 light sources are respectively used for the information recordingmedia in which the thickness of the transparent substrates aredifferent.

[0425] Further, the image pick-up apparatus in Item 64 is characterizedin that the diffraction surface is formed of a plurality of annularbands viewed from the optical axis direction, and the plurality ofannular bands are formed almost concentric circular around the opticalaxis or a point in the vicinity of the optical axis, and between thepitch Pf of the annular band corresponding to the maximum numericalaperture on the image side of the objective lens and the pitch Ph of theannular band corresponding to ½ numerical aperture in the maximumnumerical aperture, the following relationship is established:0.4≦|(Ph/Pf)−2|≦25.

[0426] According to Item 64, in the case of more than the lower limit ofthe above relationship, the action of the diffraction to correct thehigher ordered spherical aberration is not weakened, and accordingly,the difference of the spherical aberration between 2 wavelengthsgenerated by the difference of the thickness of the transparentsubstrate can be corrected by the action of the diffraction. Further, inthe case of less than the upper limit, a portion in which the pitch ofthe diffraction annular band is too small, is hardly generated, thereby,a lens which is the diffraction efficiency is high, can be produced.Further, the above-described relational expression is preferably,0.8≦|(Ph/Pf)−2|≦6.0, and more preferably, 1.2≦|(Ph/Pf)−2|≦2.0.

[0427] Further, the optical pickup apparatus in Item 65 is characterizedin that at least 2 light sources are 3 light sources.

[0428] Further, the optical pickup apparatus in Item 66 is characterizedin that, when the light having 3 different wavelengths outputted fromthe 3 light sources are respectively defined as λ1, λ2, and λ3(λ1<λ2<λ3), and the predetermined numerical apertures on the image sideof the objective lens for each of these 3 different wavelengths aredefined as NA1, NA2, and NA3, the following relationships are satisfied:0.60≦NA1, 0.60≦NA2, 0.40≦NA3<0.50.

[0429] Further, the optical pickup apparatus in Item 67 is characterizedin that a filter by which at least one portion of the light entered intothe objective lens at the outside of the smallest numerical aperture inthe predetermined numerical apertures can be shielded, is provided.

[0430] Further, the optical pickup apparatus in Item 68 is characterizedin that an aperture limitation means is provided so that thepredetermined numerical aperture can be obtained for each of the lighthaving the 2 different wavelengths.

[0431] Further, the optical pickup apparatus in Item 69 is characterizedin that there is no aperture limitation by which the predeterminednumerical aperture can be obtained for one of the light having the 2different wavelengths. For example, concretely, the maximum numericalaperture has the aperture limitation, and the aperture limitation is notprovided for the smaller predetermined numerical aperture. Thereby, theaperture limitation means such as a filter having the wavelengthselectivity is made not necessary, therefore, the cost can be lower, andthe size can be reduced.

[0432] Further, the optical pickup apparatus in Item 70 is characterizedin that the objective lens is included in the more than 1 opticalelements, and the objective lens is used in common when the light havingthe wavelengths which are different from each other, are respectivelyconverged onto the information recording medium.

[0433] Further, the optical pickup apparatus in Item 71 is characterizedin that a unit into which the at least 2 light sources and the objectare integrated, is driven at least parallelly to the main surface of theinformation recording medium.

[0434] Further, the optical pickup apparatus in Item 72 is characterizedin that the unit is vertically driven to the main surface of theinformation recording medium.

[0435] Further, Item 73 is a recording and reproducing apparatus whichis characterized in that the optical pickup apparatus is mounted, and atleast either one of an audio or an image can be recorded or played back.

[0436] Further, a lens in Item 74 is characterized in that, in the lenswhich is used for at least either one of the recording or reproducing ofthe information for the information recording medium, and has therefraction power, and the diffraction surface on at least one of theoptical surfaces, the positive and the negative signs of the diffractionpower added from the diffraction surface are switched at least one timein the direction separating from the optical axis vertically to theoptical axis.

[0437] Further, the lens in Item 75 is characterized in that, in thelens in Item 74, the diffraction surface has a plurality of blazeddiffraction annular bands, and its stepped portion is positioned at aseparated side from the optical axis in the diffraction annular band onthe near side to the optical axis, and in the diffraction annular bandon the separated side from the optical axis, its stepped portion ispositioned on a near side to the optical axis. Further, the lens in Item76 is characterized in that the diffraction surface has a plurality ofblazed diffraction annular bands, and its stepped portion is positionedon a near side to the optical axis in the diffraction annular band onthe near side to the optical axis, and in the diffraction annular bandon the separated side from the optical axis, its stepped portion ispositioned on a separated side from the optical axis.

[0438] Further, the Item 77 is an optical element which can be appliedto the optical system for recording and/or reproducing of theinformation into or from the information recording medium, the opticalelement is characterized in that, when it is used in the optical systemfor recording and/or reproducing of the information into or from theinformation recording medium, in which the light having at least 2wavelengths which are different from each other are used, it has thediffraction surface to selectively generate the same orderededdiffracted ray to the light having at least 2 wavelengths which aredifferent from each other.

[0439] Further, Item 78 is a lens which can be applied as an objectivelens in the optical system for recording and/or reproducing of theinformation into or from the information recording medium, the lens ischaracterize in that, when it is used as the objective lens in theoptical system for recording and/or reproducing of the information intoor from the information recording medium, in which the light having atleast 2 wavelengths which are different from each other are used, it hasthe diffraction surface to selectively generate the diffractionefficiency of the same ordereded diffracted ray to the light having atleast 2 wavelengths which are different from each other.

[0440] Further, Item 79 is an optical element which can be applied inthe optical system for recording and/or reproducing of the informationinto or from the information recording medium, the optical element ischaracterized in that, when it is used in the optical system forrecording and/or reproducing of the information into or from theinformation recording medium, in which the light having at least 2wavelengths which are different from each other are used, thediffraction surface to selectively generate the specific orderededdiffracted ray to the light having at least 2 wavelengths which aredifferent from each other, is formed on almost entire surface of atleast one optical surface.

[0441] Further, Item 80 is a lens which can be applied as an objectivelens in the optical system for recording and/or reproducing of theinformation into or from the information recording medium, the lens ischaracterize in that, when it is used as the objective lens in theoptical system for recording and/or reproducing of the information intoor from the information recording medium, in which the light having atleast 2 wavelengths which are different from each other are used, thediffraction surface to selectively generate the specific orderededdiffracted ray to the light having at least 2 wavelengths which aredifferent from each other, is formed on almost entire surface of atleast one optical surface.

[0442] Further, a diffraction optical system for the optical disk inItem 81 is characterized in that, in the recording and reproducingoptical system which has 2 light source having different wavelengths andrecords and plays back by the same optical system, the optical systemincludes the optical surface on which the diffraction annular band lensis provided on the refraction surface, and the aberration generated bythe difference of the wavelength on the refraction surface and theaberration generated by the diffraction annular band lens are cancelled,and the diffracted ray used for the canceling is the same orderededdiffracted ray to the wavelengths of 2 light source.

[0443] As described above, this diffraction optical system ischaracterized in that it includes the optical surface on which thediffraction annular band lens is provided on the refraction surface, andto each of the light sources having 2 different wavelengths, a certain 1same ordereded diffracted ray and the spherical aberration by thediffraction surface are cancelled, thereby, these are corrected to noaberration, which is almost equal to the diffraction limit. The sameordereded diffracted ray is preferably first ordered diffracted ray.

[0444] A method to make the same ordereded diffracted ray to correspondto each wavelength of 2 light sources as the present invention, has anadvantage in which totally the loss of the light amount is smaller, ascompared to the case in which the diffracted ray of the differentordered is made to correspond to. For example, in the case where 2wavelengths of 780 nm and 635 nm are used, when the first ordereddiffracted ray is used for the light of both wavelengths, totally theloss of the light amount is smaller than the case in which the firstordered diffracted ray is used for one wavelength, and the zero ordereddiffracted ray is used for the other wavelength. Further, in the casewhere the same ordered diffracted ray is used for the light of bothwavelength, when the first ordered diffracted ray is used, the loss ofthe light amount is smaller than the case where high orderededdiffracted ray is used.

[0445] Further, a diffraction optical system for an optical disk in Item82 is characterized in that the canceled aberration is the sphericalaberration and/or the chromatic aberration.

[0446] Further, a diffraction optical system for an optical disk in Item83 is characterized in that the diffracted ray of the same ordered isthe first ordered diffracted ray.

[0447] Further, a diffraction optical system for an optical disk in Item84 is characterized in that the light sources of 2 different wavelengthscorrespond to the optical disks whose transparent substrate thicknessare respectively different.

[0448] Further, a diffraction optical system for an optical disk in Item85 is characterized in that the wavelength of the light source of theshorter wavelength in 2 wavelengths which are different from each otheris not larger than 700 nm.

[0449] Further, a diffraction optical system for an optical disk in Item86 is characterized in that the wavelength of the light source of thelonger wavelength in 2 wavelengths which are different from each otheris not shorter than 600 nm.

[0450] Further, a diffraction optical system for an optical disk in Item87 is characterized in that, in the diffraction annular band lens, thephase function expressing the position of the annular band includesfactors of terms except second power of power series.

[0451] Further, a diffraction optical system for an optical disk in Item88 is characterized in that the optical refraction surface isaspherical.

[0452] Further, a diffraction optical system for an optical disk in Item89 is characterized in that, to the light sources of 2 differentwavelengths which are different from each other, the diffractionefficiency of the diffracted ray is maximum at the almost intermediatewavelength thereof.

[0453] Further, a diffraction optical system for an optical disk in Item90 is characterized in that, to the light sources of 2 differentwavelengths which are different from each other, the diffractionefficiency of the diffracted ray is maximum at one of wavelengths of thelight sources.

[0454] Further, a diffraction optical system for an optical disk in Item91 is characterized in that, in the diffraction annular band lens on theoptical surface, the spherical aberration is corrected to an undervalue, and in the aspherical surface of the optical surface, thespherical aberration is corrected to an over value.

[0455] Further, in a diffraction optical system for an optical disk inItem 91, when the objective lens is used for the parallel lightincidence for both of, for example, CD system (for example, thewavelength is 780 nm, the substrate thickness is 1.2 mm) and DVD system(for example, the wavelength is 650 nm, the substrate thickness is 0.6mm), in the CD system, because the thickness of the substrate is thick,the spherical aberration has an over value compared to that of DVDsystem, however, because this spherical aberration is corrected by thedifference of the wavelength of the diffraction lens, the sphericalaberration of the diffraction lens is made under. Incidentally, in thiscase, in the long wavelength of the CD system, the spherical aberrationof the diffraction lens becomes largely under, therefore, the influencedue to the thickness of the substrate is corrected. In the asphericalsurface, the influence of the difference of the substrate thickness isnot corrected, and in both of the CD system and DVD system, thespherical aberration is overly corrected to almost the same degree. Inthe above description, it is utilized that, when high ordered terms ofthe diffraction are used, the wave motion of the spherical aberrationcan be largely controlled.

[0456] Further, in a diffraction optical system for an optical disk inItem 92, its difference of the wavelength is not less than 80 nm in thelight sources having 2 different wavelengths.

[0457] Further, a diffraction optical system for an optical disk in Item93 is characterized in that, in the objective lens optical system of theoptical disk, when the diffraction annular band lens is provided on theoptical surface, the axial chromatic aberration of a certain one of thesame ordereded diffracted ray is corrected to each of the light sourceshaving 2 different wavelengths.

[0458] Further, a diffraction optical system for an optical disk in Item94 is characterized in that the difference of the wavelengths of thelight sources having 2 different wavelengths is not less than 80 nm, andthe diffraction optical system has a single objective lens whichsatisfies the following relationship: νd>50, where, νd is Abbe's numberof the glass material of the objective lens.

[0459] Further, a diffraction optical system for an optical disk in Item95 is characterized in that, in the lens performance to 2 differentwavelengths, either one is no-aberration up to the aperture in thepractical use, and in its outside portion, the aberration is made aflare.

[0460] Further, a diffraction optical system for an optical disk in Item96 is characterized in that, in the lens performance to 2 differentwavelengths, when the numerical number to the wavelength which isno-aberration in the open aperture, is defined as NA1, and the numericalaperture of the other wavelength in the practical use is defined as NA2,the following relationship is satisfied: NA1>NA2>0.5×NA1.

[0461] Further, a diffraction optical system for an optical disk in Item97 is characterized in that the thickness of the optical disk to the 2different wavelengths is different.

[0462] Further, a optical pickup apparatus in Item 98 is a opticalpickup apparatus used for the recording and reproducing optical systemwhich has at least more than 2 light sources having the differentwavelengths, and in which the divergent light flux from each of lightsources is used for recording the information onto and/or reproducingthe information on the information recording surface of the opticalinformation recording medium by the same one objective lens through thetransparent substrate, the optical pickup apparatus in Item 98 ischaracterized in that the objective lens includes the optical surface inwhich the ring band-like diffraction surface is provided on therefraction surface, and to at least 1 light source, the light fluxtransmitted through the objective lens and the transparent substrate hasthe diffraction limit performance at the best image point.

[0463] Herein, the diffraction limit performance means that the wavefront aberration is measured, and the root mean square value (rms value)of the wave front aberration of the entire light flux is not more than0.07 times of the wavelength which is Mareshal's allowance. Further, theaperture in the practical use means the numerical aperture which isregulated by respective standards of the optical information recordingmedium, and corresponds to the numerical aperture of the objective lensof the diffraction limit performance by which the spot diameternecessary for recording or reproducing of the information to respectiveoptical information recording media, can be obtained.

[0464] As described above, because the numerical aperture in thepractical use is regulated to the optical information recording medium,the numerical aperture on the optical information recording medium sideof the actual light flux passing through the optical system of thepick-up apparatus may be larger than the numerical aperture in thepractical use.

[0465] Further, in the present invention, it may be preferable that themaximum numerical aperture preferably means the maximum one in thenumerical aperture in the practical use. That is, in the case of thepick-up apparatus interchangeably used for a plurality of opticalinformation recording media, a plurality of numerical apertures in thepractical use are defined, and it may be preferable that the maximum onein these numerical apertures is defined as the maximum numericalaperture. Further, a predetermined numerical aperture and necessarynumerical aperture are the same meaning as the numerical aperture in thepractical use.

[0466] Incidentally, in the case where the information is recorded ontoor played back from the optical information recording medium, when thelight source having the different wavelength from that of the lightsource regulated by the standard is used in the actual optical pickupapparatus, the actually used numerical aperture is set so that the ratioof the regulated wavelength and the regulated numerical aperture, andthe ratio of the actually used wavelength and the actually usednumerical aperture, becomes constant. As an example, in the CD, when thelight source with 780 nm wavelength in the standard is used, thenumerical aperture is 0.45, however, when the light source with 650 nmwavelength is used, the numerical aperture is 0.38.

[0467] Further, a optical pickup apparatus in Item 99 is a opticalpickup apparatus used for the recording and reproducing optical systemwhich has at least more than 2 light sources having the differentwavelengths, and in which the divergent light flux from each of lightsources is used for recording the information onto and/or reproducingthe information on the information recording surface of the opticalinformation recording medium by the same one objective lens through thetransparent substrate, the optical pickup apparatus in Item 99 ischaracterized in that the objective lens includes the optical surface inwhich the ring band-like diffraction surface is provided on therefraction surface, and to at least 1 light source, the light fluxtransmitted through the objective lens and the transparent substrate hasthe diffraction limit performance at the best image point, and to atleast 1 light source, in the light flux transmitted through theobjective lens and the transparent substrate, the light flux up to theaperture in the practical use has the diffraction limit performance atthe best image point, and the ring band-like diffraction surface isprovided so that the outside portion thereof becomes the flare.

[0468] Further, the optical pickup apparatus in Item 100 ischaracterized in that the above-described apparatus has at least 3 lightsources having different wavelengths.

[0469] Further, the optical pickup apparatus in Item 101 ischaracterized in that the above-described apparatus includes the opticalsurface on which at least more than 2 ring band-like diffractionsurfaces are provided.

[0470] Further, the optical pickup apparatus in Item 102 ischaracterized in that the above-described apparatus includes a ringband-like filter to shield a portion of the light flux outside of theactually used aperture in the light flux entering into the objectivelens.

[0471] Further, the optical pickup apparatus in Item 103 ischaracterized in that, in the above-described apparatus, the unitincluding the light source and the objective lens, is driven parallelyat least to the optical information recording medium.

[0472] Further, the optical pickup apparatus in Item 104 ischaracterized in that, in the above-described apparatus, the unitincluding the light source and the objective lens, is further drivenvertically to the optical information recording medium.

[0473] Further, the invention according to Item 105 is an audio and/orimage recording, and/or an audio and/or image reproducing apparatuscharacterized in that the above-described optical pickup apparatus ismounted.

[0474] Further, an objective lens in Item 106 is an objective lens usedfor the recording and reproducing optical system which has at least morethan 2 light sources having the different wavelengths, and in which thedivergent light flux from each of light sources is used for recordingthe information onto and/or reproducing the information on theinformation recording surface of the optical information recordingmedium by the same one objective lens through the transparent substrate,the objective lens is characterized in that it includes the opticalsurface in which the ring band-like diffraction surface is provided onthe refraction surface, and to at least 1 light source, the light fluxtransmitted through the objective lens and the transparent substrate hasthe diffraction limit performance at the best image point.

[0475] Further, an objective lens in Item 107 is an objective lens usedfor the recording and reproducing optical system which has at least morethan 2 light sources having the different wavelengths, and in which thedivergent light flux from each of light sources is used for recordingthe information onto and/or reproducing the information on theinformation recording surface of the optical information recordingmedium by the same one objective lens through the transparent substrate,the objective lens is characterized in that it includes the opticalsurface in which the ring band-like diffraction surface is provided onthe refraction surface, and to at least 1 light source, the light fluxtransmitted through the objective lens and the transparent substrate hasthe diffraction limit performance at the best image point, and to atleast 1 light source, in the light flux transmitted through theobjective lens and the transparent substrate, the light flux up to theaperture in the practical use has the diffraction limit performance atthe best image point, and the ring band-like diffraction surface isprovided so that the outside portion thereof becomes the flare.

[0476] Further, the optical pickup apparatus in Item 108 in which thelight flux emitted from the light source is converged onto theinformation recording surface by the light converging optical systemincluding the objective lens through the transparent substrate of theoptical information recording medium, and which has the first lightsource having the wavelength λ1 to record/reproducing the first opticalinformation recording medium, the second light source having thewavelength λ2 to record/reproducing the second optical informationrecording medium, and the third light source having the wavelength λ3 torecord/reproducing the third optical information recording medium, whosewavelengths are different from each other, and records and plays backthe optical information recording medium, the optical pickup apparatusis characterized in that, on at least one surface of the objective lens,the diffraction surface by which the spherical aberration is correctedto almost the same degree as the diffraction limit or smaller than it bya certain same ordereded diffracted ray to each of optical informationrecording media, is formed.

[0477] Further, the optical pickup apparatus in Item 109 in which thelight flux emitted from the light source is converged onto theinformation recording surface by the light converging optical systemincluding the objective lens through the transparent substrate of theoptical information recording medium, and which has the first lightsource having the wavelength λ1 to record/reproducing the first opticalinformation recording medium, the second light source having thewavelength λ2 to record/reproducing the second optical informationrecording medium, and the third light source having the wavelength λ3 torecord/reproducing the third optical information recording medium, whosewavelengths are different from each other, and records and plays backthe optical information recording medium, the optical pickup apparatusis characterized in that, on at least one surface of the objective lens,a certain same ordereded diffracted ray is used for each of opticalinformation recording media, and for at least one optical informationrecording medium, the aberration up to the aperture in the practical useis made to almost the same degree as the diffraction limit or smallerthan it, and the aberration in a portion outside the aperture is made tothe flare.

[0478] In the optical pickup apparatus in Item 109 to record and/orreproduce the optical information recording medium, the objective lensformed the diffraction surface uses a certain same ordereded diffractedray for each of optical information recording media, and for at leastone optical information recording medium, the aberration up to theaperture in the practical use is made to almost the same degree as thediffraction limit or smaller than it, and the aberration in a portionoutside the aperture is made to the flare.

[0479] Further, as will be described in following Items, it ispreferable that the diffraction surface is formed on both surfaces ofthe objective lens, and the diffracted ray is the first ordereddiffracted ray. The following is characterized: the diffraction surfaceis formed to ring band-like around the optical axis of the objectivelens, and the phase function to express the position of the annular bandincludes factors of terms except 2 power term in the power series,however, the phase function may include the 2 power term in the powerseries, or may not include it. Further, it is preferable that, in thediffraction surface, the diffraction efficiency of the diffracted ray ismaximum in the wavelength of both ends or of intermediate area, to eachof the first light source, the second light source, and the third lightsource. Further, the objective lens has at least one surface which isaspherical, and the spherical aberration is corrected to under on thediffraction surface, and the spherical aberration is corrected to overon the aspherical surface, thereby, the above-described function can beprovided.

[0480] Further, the optical pickup apparatus in Item 110 ischaracterized in that the diffraction surface is formed on both sides ofthe objective lens.

[0481] Further, the optical pickup apparatus in Item 111 ischaracterized in that the same ordereded diffracted ray is the firstordered diffracted ray.

[0482] Further, the optical pickup apparatus in Item 112 ischaracterized in that the diffraction surface is formed to ringband-like around the optical axis of the objective lens, and the phasefunction to express the position of the annular band includes thefactors of terms except the second power term in the power series.

[0483] Further, the optical pickup apparatus in Item 113 ischaracterized in that the diffraction surface is formed to ringband-like around the optical axis of the objective lens, and the phasefunction to express the position of the annular band includes the factorof the second power term in the power series.

[0484] Further, the optical pickup apparatus in Item 114 ischaracterized in that the diffraction surface is formed to ringband-like around the optical axis of the objective lens, and the phasefunction to express the position of the annular band does not includethe factor of the second power term in the power series.

[0485] Further, the optical pickup apparatus in Item 115 ischaracterized in that the diffraction efficiency of the diffracted rayis maximum in the wavelength of both ends or of intermediate area, toeach of the first light source, the second light source, and the thirdlight source.

[0486] Further, the optical pickup apparatus in Item 116 ischaracterized in that at least one surface of the objective lens isaspherical, and the spherical aberration is corrected to under on thediffraction surface, and the spherical aberration is corrected to overon the aspherical surface.

[0487] Further, the invention in Item 117 is an audio and/or imagewriting, and/or an audio and/or image reproducing apparatus, which ischaracterized in that the optical pickup apparatus described in any ofItems 108-116 having the first light source, the second light source andthe third light source, is mounted.

[0488] Further, an objective lens in Item 118 used for the opticalpickup apparatus in which the light flux emitted from the light sourceis converged onto the information recording surface by the lightconverging optical system through the transparent substrate of theoptical information recording medium, and which has the first lightsource having the wavelength λ1 to record/reproducing the first opticalinformation recording medium, the second light source having thewavelength λ2 to record/reproducing the second optical informationrecording medium, and the third light source having the wavelength λ3 torecord/reproducing the third optical information recording medium, whosewavelengths are different from each other, and records and plays backthe optical information recording medium, the objective lens ischaracterized in that, on at least one surface of the objective lens,the diffraction surface is formed, in which the spherical aberration iscorrected by a certain same ordereded diffracted ray for each of opticalinformation recording media, to almost the same degree as thediffraction limit or smaller than it.

[0489] Further, an objective lens in Item 119 used for the opticalpickup apparatus in which the light flux emitted from the light sourceis converged onto the information recording surface by the lightconverging optical system through the transparent substrate of theoptical information recording medium, and which has the first lightsource having the wavelength λ1 to record/reproducing the first opticalinformation recording medium, the second light source having thewavelength λ2 to record/reproducing the second optical informationrecording medium, and the third light source having the wavelength λ3 torecord/reproducing the third optical information recording medium, whosewavelengths are different from each other, and records and plays backthe optical information recording medium, the objective lens ischaracterized in that, on at least one surface of the objective lens, acertain same ordereded diffracted ray is used for each of opticalinformation recording media, and to at least one optical informationrecording medium, the spherical aberration is corrected up to theaperture in the practical use to almost the same degree as thediffraction limit or smaller than it, and to the portion outside it, theaberration is made to the flare.

[0490] Further, the optical pickup apparatus in Item 120 in which thelight flux emitted from the light source is converged onto theinformation recording surface by the light converging optical systemthrough the transparent substrate of the optical information recordingmedium, and which has the first light source having the wavelength λ1 torecord/reproducing the first optical information recording medium, thesecond light source having the wavelength λ2 to record/reproducing thesecond optical information recording medium, and the third light sourcehaving the wavelength λ3 to record/reproducing the third opticalinformation recording medium, whose wavelengths are different from eachother, and records and plays back the optical information recordingmedium, the optical pickup apparatus is characterized in that, on atleast one surface of the light converging optical system, thediffraction surface is formed, in which the spherical aberration iscorrected by a certain same ordereded diffracted ray for each of opticalinformation recording media, to almost the same degree as thediffraction limit or smaller than it.

[0491] Further, the optical pickup apparatus in Item 121 in which thelight flux emitted from the light source is converged onto theinformation recording surface by the light converging optical systemthrough the transparent substrate of the optical information recordingmedium, and which has the first light source having the wavelength λ1 torecord/reproducing the first optical information recording medium, thesecond light source having the wavelength λ2 to record/reproducing thesecond optical information recording medium, and the third light sourcehaving the wavelength λ3 to record/reproducing the third opticalinformation recording medium, whose wavelengths are different from eachother, and records and plays back the optical information recordingmedium, the optical pickup apparatus is characterized in that, on atleast one surface of the light converging optical system, thediffraction surface is provided, in which a certain same orderededdiffracted ray is used for each of optical information recording media,and for at least one optical information recording medium, theaberration is corrected to almost the same degree as the diffractionlimit or smaller than it, up to the aperture in the practical use, andto the portion outside it, the aberration is made to the flare.

[0492] Further, the optical pickup apparatus in Item 122 has: the firstlight source with the wavelength λ1, the second light source with thewavelength λ2 (λ2≢λ1); the objective lens which has the diffractionpattern on at least one surface, and converges the light flux from eachof the light sources onto the information recording surface of theoptical information recording medium through the transparent substrate;and the light detector to receive the reflected light of the emittedlight flux from the first light source and the second light source fromthe optical information recording medium, and when, at least, them-ordered diffracted ray (m is an integer except 0) from the diffractionpattern of the objective lens of the light flux from the first lightsource is used, the first optical information recording medium, in whichthe thickness of the transparent substrate is t1, is recorded and/orplayed back, and when, at least, the n-th ordered diffracted ray (n=m)from the diffraction pattern of the objective lens of the light fluxfrom the first light source is used, the second optical informationrecording medium, in which the thickness of the transparent substrate ist2 (t2≢t1), is recorded and/or played back.

[0493] Further, the optical pickup apparatus in Item 123 is a opticalpickup apparatus used in the relationship in which the wavelengths λ1and λ2 of the first and the second light sources are λ1<λ2, and thethickness of the transparent substrate t1 and t2 are t1<t2, the opticalpickup apparatus is characterized in that the m-ordered and n-th ordereddiffracted ray are both +first ordered diffracted ray.

[0494] Further, the optical pickup apparatus in Item 124 is a opticalpickup apparatus used in the relationship in which the wavelengths λ1and λ2 of the first and the second light sources are λ1<λ2, and thethickness of the transparent substrate t1 and t2 are t1>t2, the opticalpickup apparatus is characterized in that the m-ordered and n-th ordereddiffracted ray are both −first ordered diffracted ray.

[0495] Further, the optical pickup apparatus in Item 125 ischaracterized in that, in the apparatus in Item 122, when the necessarynumerical aperture on the optical information recording medium side ofthe objective lens required for recording and/or reproducing the firstoptical information recording medium in which the thickness of thetransparent substrate is t1, by the first light source with thewavelength λ1, is defined as NA1, and the necessary numerical apertureon the optical information recording medium side of the objective lensrequired for recording and/or reproducing the second optical informationrecording medium in which the thickness of the transparent substrate ist2 (t2>t1), by the second light source with the wavelength λ2 (λ2>λ1),is defined as NA2 (NA2<NA1), the diffraction pattern provided on atleast one surface of the objective lens is the rotation symmetry to theoptical axis, and +first ordered diffracted ray from the circumferencemost separated from the optical axis of the diffraction pattern of theobjective lens of the light flux from the first light source isconverted into the light flux whose numerical aperture on the opticalinformation recording medium side is NAH1, and +first ordered diffractedray from the circumference nearest to the optical axis side of thediffraction pattern of the objective lens of the light flux from thefirst light source is converted into the light flux whose numericalaperture on the optical information recording medium side is NAL1, andthe following relationship is satisfied:

NAH1<NA1, 0≦NAL1≦NA2.

[0496] Further, the optical pickup apparatus in Item 126 ischaracterized in that, in the apparatus in Item 122, when the necessarynumerical aperture on the optical information recording medium side ofthe objective lens required for recording and/or reproducing the firstoptical information recording medium in which the thickness of thetransparent substrate is t1, by the first light source with thewavelength λ1, is defined as NA1, and the necessary numerical apertureon the optical information recording medium side of the objective lensrequired for recording and/or reproducing the second optical informationrecording medium in which the thickness of the transparent substrate ist2 (t2>t1), by the second light source with the wavelength λ2 (λ2>λ1),is defined as NA2 (NA2>NA1), the diffraction pattern provided on atleast one surface of the objective lens is the rotation symmetry to theoptical axis, and +first ordered diffracted ray from the circumferencemost separated from the optical axis of the diffraction pattern of theobjective lens of the light flux from the first light source isconverted into the light flux whose numerical aperture on the opticalinformation recording medium side is NAH1, and +first ordered diffractedray from the circumference nearest to the optical axis side of thediffraction pattern of the objective lens of the light flux from thefirst light source is converted into the light flux whose numericalaperture on the optical information recording medium side is NAL1, andthe following relationship is satisfied:

NAH1<NA2, 0≦NAL1≦NA1.

[0497] Further, the optical pickup apparatus in Item 127 ischaracterized in that, in the apparatus in Item 122, when the necessarynumerical aperture on the optical information recording medium side ofthe objective lens required for recording and/or reproducing the firstoptical information recording medium in which the thickness of thetransparent substrate is t1, by the first light source with thewavelength λ1, is defined as NA1, and the necessary numerical apertureon the optical information recording medium side of the objective lensrequired for recording and/or reproducing the second optical informationrecording medium in which the thickness of the transparent substrate ist2 (t2<t1), by the second light source with the wavelength λ2 (λ2>λ1),is defined as NA2 (NA2<NA1), the diffraction pattern provided on atleast one surface of the objective lens is the rotation symmetry to theoptical axis, and −first ordered diffracted ray from the circumferencemost separated from the optical axis of the diffraction pattern of theobjective lens of the light flux from the first light source isconverted into the light flux whose numerical aperture on the opticalinformation recording medium side is NAH1, and −first ordered diffractedray from the circumference nearest to the optical axis side of thediffraction pattern of the objective lens of the light flux from thefirst light source is converted into the light flux whose numericalaperture on the optical information recording medium side is NAL1, andthe following relationship is satisfied:

NAH1<NA1, 0≦NAL1≦NA2.

[0498] Further, the optical pickup apparatus in Item 128 ischaracterized in that, in the apparatus in Item 122, when the necessarynumerical aperture on the optical information recording medium side ofthe objective lens required for recording and/or reproducing the firstoptical information recording medium in which the thickness of thetransparent substrate is t1, by the first light source with thewavelength λ1, is defined as NA1, and the necessary numerical apertureon the optical information recording medium side of the objective lensrequired for recording and/or reproducing the second optical informationrecording medium in which the thickness of the transparent substrate ist2 (t2<t1), by the second light source with the wavelength λ2 (λ2>λ1),is defined as NA2 (NA2>NA1), the diffraction pattern provided on atleast one surface of the objective lens is the rotation symmetry to theoptical axis, and −first ordered diffracted ray from the circumferencemost separated from the optical axis of the diffraction pattern of theobjective lens of the light flux from the first light source isconverted into the light flux whose numerical aperture on the opticalinformation recording medium side is NAH1, and −first ordered diffractedray from the circumference nearest to the optical axis side of thediffraction pattern of the objective lens of the light flux from thefirst light source is converted into the light flux whose numericalaperture on the optical information recording medium side is NAL1, andthe following relationship is satisfied:

NAH1<NA2, 0≦NAL1≦NA1.

[0499] Further, the optical pickup apparatus in Item 129 ischaracterized in that, in the apparatus in Item 125, in the light fluxfrom the first light source, the light converging position of the lightflux whose numerical aperture is not more than NA1 when the light fluxpasses through the objective lens and which does not pass through thediffraction pattern, is almost the same as the light converging positionof the light flux which passes through the diffraction pattern.

[0500] Further, the optical pickup apparatus in Item 130 ischaracterized in that, in the apparatus in Item 126, in the light fluxfrom the second light source, the light converging position of the lightflux whose numerical aperture is not more than NA2 when the light fluxpasses through the objective lens and which does not passes through thediffraction pattern, is almost the same as the light converging positionof the light flux which passes through the diffraction pattern.

[0501] Further, the optical pickup apparatus in Item 131 ischaracterized in that, in the apparatus in Item 127, in the light fluxfrom the first light source, the light converging position of the lightflux whose numerical aperture is not more than NA1 when the light fluxpasses through the objective lens and which does not pass through thediffraction pattern, is almost the same as the light converging positionof the light flux which passes through the diffraction pattern.

[0502] Further, the optical pickup apparatus in Item 132 ischaracterized in that, in the apparatus in Item 128, in the light fluxfrom the second light source, the light converging position of the lightflux whose numerical aperture is not more than NA2 when the light fluxpasses through the objective lens and which does not passes through thediffraction pattern, is almost the same as the light converging positionof the light flux which passes through the diffraction pattern.

[0503] Further, the optical pickup apparatus in Item 133 ischaracterized in that, in the apparatus in Item 129, +first ordereddiffracted ray from the circumference most separated from the opticalaxis of the diffraction pattern of the objective lens of the light fluxfrom the second light source is converted into the light flux whosenumerical aperture on the optical information recording medium side isNAH2, and +first ordered diffracted ray from the circumference nearestto the optical axis of the diffraction pattern of the objective lens ofthe light flux from the second light source is converted into the lightflux whose numerical aperture on the optical information recordingmedium side is NAL2, and the spherical aberration of the light fluxwhich passes through the objective lens is set such that, in the lightflux from the first light source, the light flux whose numericalaperture is not more than NA1 when the light flux passes through theobjective lens is used and spots are converged on the informationrecording surface of the optical information recording medium so thatrecording and/or reproducing of the first optical information recordingmedium can be conducted, and in the light flux from the second lightsource, the light flux whose numerical aperture is not more than NAH2when the light flux passes through the objective lens is used and spotsare converged on the information recording surface of the opticalinformation recording medium so that recording and/or reproducing of thesecond optical information recording medium can be conducted.

[0504] Further, the optical pickup apparatus in Item 134 ischaracterized in that, in the apparatus in Item 130, +first ordereddiffracted ray from the circumference most separated from the opticalaxis of the diffraction pattern of the objective lens of the light fluxfrom the second light source is converted into the light flux whosenumerical aperture on the optical information recording medium side isNAH2, and +first ordered diffracted ray from the circumference nearestto the optical axis of the diffraction pattern of the objective lens ofthe light flux from the second light source is converted into the lightflux whose numerical aperture on the optical information recordingmedium side is NAL2, and the spherical aberration of the light fluxwhich passes through the objective lens is set such that, in the lightflux from the first light source, the light flux whose numericalaperture is not more than NAH1 when the light flux passes through theobjective lens is used and spots are converged on the informationrecording surface of the optical information recording medium so thatrecording and/or reproducing of the first optical information recordingmedium can be conducted, and in the light flux from the second lightsource, the light flux whose numerical aperture is not more than NA2when the light flux passes through the objective lens is used and spotsare converged on the information recording surface of the opticalinformation recording medium so that recording and/or reproducing of thesecond optical information recording medium can be conducted.

[0505] Further, the optical pickup apparatus in Item 135 ischaracterized in that, in the apparatus in Item 131, −first ordereddiffracted ray from the circumference most separated from the opticalaxis of the diffraction pattern of the objective lens of the light fluxfrom the second light source is converted into the light flux whosenumerical aperture on the optical information recording medium side isNAH2, and −first ordered diffracted ray from the circumference nearestto the optical axis of the diffraction pattern of the objective lens ofthe light flux from the second light source is converted into the lightflux whose numerical aperture on the optical information recordingmedium side is NAL2, and the spherical aberration of the light fluxwhich passes through the objective lens is set such that, in the lightflux from the first light source, the light flux whose numericalaperture is not more than NA1 when the light flux passes through theobjective lens, is used, and spots are converged on the informationrecording surface of the optical information recording medium so thatrecording and/or reproducing of the first optical information recordingmedium can be conducted, and in the light flux from the second lightsource, the light flux whose numerical aperture is not more than NAH2when the light flux passes through the objective lens, is used, andspots are converged on the information recording surface of the opticalinformation recording medium so that recording and/or reproducing of thesecond optical information recording medium can be conducted.

[0506] Further, the optical pickup apparatus in Item 136 ischaracterized in that, in the apparatus in Item 132, −first ordereddiffracted ray from the circumference most separated from the opticalaxis of the diffraction pattern of the objective lens of the light fluxfrom the second light source is converted into the light flux whosenumerical aperture on the optical information recording medium side isNAH2, and −first ordered diffracted ray from the circumference nearestto the optical axis of the diffraction pattern of the objective lens ofthe light flux from the second light source is converted into the lightflux whose numerical aperture on the optical information recordingmedium side is NAL2, and the spherical aberration of the light fluxwhich passes through the objective lens is set such that, in the lightflux from the first light source, the light flux whose numericalaperture is not more than NAH1 when the light flux passes through theobjective lens is used and spots are converged on the informationrecording surface of the optical information recording medium so thatrecording and/or reproducing of the first optical information recordingmedium can be conducted, and in the light flux from the second lightsource, the light flux whose numerical aperture is not more than NA2when the light flux passes through the objective lens is used and spotsare converged on the information recording surface of the opticalinformation recording medium so that recording and/or reproducing of thesecond optical information recording medium can be conducted.

[0507] Further, the optical pickup apparatus in Item 137 ischaracterized in that, in the apparatus in Item 133, in the light fluxfrom the first light source, the wave front aberration of the light fluxwhose numerical aperture is not more than NA1 when the light flux passesthrough the objective lens, at the best image point through thetransparent substrate of the first optical information recording mediumis not more than 0.07 λrms, and in the light flux from the second lightsource, the wave front aberration of the light flux whose numericalaperture is not more than NAH2 when the light flux passes through theobjective lens, at the best image point through the transparentsubstrate of the second optical information recording medium is not morethan 0.07 λrms.

[0508] Further, the optical pickup apparatus in Item 138 ischaracterized in that, in the apparatus in Item 134, in the light fluxfrom the first light source, the wave front aberration of the light fluxwhose numerical aperture is not more than NAH1 when the light fluxpasses through the objective lens, at the best image point through thetransparent substrate of the first optical information recording mediumis not more than 0.07 arms, and in the light flux from the second lightsource, the wave front aberration of the light flux whose numericalaperture is not more than NA2 when the light flux passes through theobjective lens, at the best image point through the transparentsubstrate of the second optical information recording medium is not morethan 0.07 arms.

[0509] Further, the optical pickup apparatus in Item 139 ischaracterized in that, in the apparatus in Item 135, in the light fluxfrom the first light source, the wave front aberration of the light fluxwhose numerical aperture is not more than NA1 when the light flux passesthrough the objective lens, at the best image point through thetransparent substrate of the first optical information recording mediumis not more than 0.07 λrms, and in the light flux from the second lightsource, the wave front aberration of the light flux whose numericalaperture is not more than NAH2 when the light flux passes through theobjective lens, at the best image point through the transparentsubstrate of the second optical information recording medium is not morethan 0.07 λrms.

[0510] Further, the optical pickup apparatus in Item 140 ischaracterized in that, in the apparatus in Item 136, in the light fluxfrom the first light source, the wave front aberration of the light fluxwhose numerical aperture is not more than NAH1 when the light fluxpasses through the objective lens, at the best image point through thetransparent substrate of the first optical information recording mediumis not more than 0.07 λrms, and in the light flux from the second lightsource, the wave front aberration of the light flux whose numericalaperture is not more than NA2 when the light flux passes through theobjective lens, at the best image point through the transparentsubstrate of the second optical information recording medium is not morethan 0.07 λrms.

[0511] Further, the optical pickup apparatus in Item 141 ischaracterized in that, in the apparatus in any one Item of Items122-140, at least one collimator is included between the first lightsource and the objective lens, and between the second light source andthe objective lens, and the light flux entering into the objective lensfrom the first light source and the light flux entering into theobjective lens from the second light source are respectively parallellight.

[0512] Further, the optical pickup apparatus in Item 142 ischaracterized in that, in the apparatus in Item 141, the paraxial focusposition of the objective lens for the light flux form the first lightsource and the paraxial focus position of the objective lens for thelight flux from the second light source almost coincide with each other.

[0513] Further, the optical pickup apparatus in Item 143 ischaracterized in that, in the apparatus in Items 129, 133 and 137, thesecond diffraction pattern is provided outside the diffraction pattern,and the second diffraction pattern is set such that +first ordereddiffracted ray of the second diffraction pattern to the light flux fromthe first light source is converged onto the light converging position,and the light flux from the second light source is not diffracted by thesecond diffraction pattern.

[0514] Further, the optical pickup apparatus in Item 144 ischaracterized in that, in the apparatus in Items 130, 134 and 138, thesecond diffraction pattern is provided outside the diffraction pattern,and the second diffraction pattern is set such that the light flux fromthe first light source becomes mainly +first ordered diffracted ray inthe second diffraction pattern, and the light flux from the second lightsource is transmitted through the second diffraction pattern and isconverged onto the light converging position.

[0515] Further, the optical pickup apparatus in Item 145 ischaracterized in that, in the apparatus in Items 131, 135 and 139, thesecond diffraction pattern is provided outside the diffraction pattern,and the second diffraction pattern is set such that −first ordereddiffracted ray in the second diffraction pattern is converged onto thelight converging position to the light flux from the first light source,and the light flux from the second light source is not diffracted by thesecond diffraction pattern.

[0516] Further, the optical pickup apparatus in Item 146 ischaracterized in that, in the apparatus in Items 132, 136 and 140, thesecond diffraction pattern is provided outside the diffraction pattern,and the second diffraction pattern is set such that the light flux fromthe first light source becomes mainly −first ordered diffracted ray inthe second diffraction pattern, and the light flux from the second lightsource is transmitted through the second diffraction pattern and isconverged onto the light converging position.

[0517] Further, the optical pickup apparatus in Item 147 ischaracterized in that, in the apparatus in Items 129, 133 and 137, thesecond diffraction pattern is provided outside the diffraction pattern,and the second diffraction pattern is set such that the transmittedlight of the second diffraction pattern to the light flux from the firstlight source is converged onto the light converging position, and thelight flux from the second light source becomes mainly −first ordereddiffracted ray in the second diffraction pattern.

[0518] Further, the optical pickup apparatus in Item 148 ischaracterized in that, in the apparatus in Items 130, 134 and 138, thesecond diffraction pattern is provided outside the diffraction pattern,and the second diffraction pattern is set such that the light flux fromthe first light source passes through the second diffraction pattern,and the light flux from the second light source becomes mainly −firstordered diffracted ray in the second diffraction pattern, and isconverged onto the light converging position.

[0519] Further, the optical pickup apparatus in Item 149 ischaracterized in that, in the apparatus in Items 131, 135 and 139, thesecond diffraction pattern is provided outside the diffraction pattern,and the second diffraction pattern is set such that the transmittedlight of the second diffraction pattern to the light flux from the firstlight source is converged onto the light converging position, and thelight flux from the second light source becomes mainly +first ordereddiffracted ray in the second diffraction pattern.

[0520] Further, the optical pickup apparatus in Item 150 ischaracterized in that, in the apparatus in Items 132, 136 and 140, thesecond diffraction pattern is provided outside the diffraction pattern,and the second diffraction pattern is set such that the light flux fromthe first light source passes through the second diffraction pattern,and the light flux from the second light source becomes mainly +firstordered diffracted ray in the second diffraction pattern, and isconverged onto the light converging position.

[0521] Further, the optical pickup apparatus in Item 151 ischaracterized in that, in the apparatus in Items 129, 131, 133, 135 137or 139, the apparatus includes a light wave composing means by which theemitted light flux from the first light source and the emitted lightflux from the second light source can be composed, and has the openinglimiting means which transmits the light flux from the first lightsource, and in the light flux from the second light source, which doesnot transmit the flux which passes through the opposite side area to theoptical axis of the diffraction pattern, between the light wavecomposing means and the optical information recording medium.

[0522] Further, the optical pickup apparatus in Item 151 ischaracterized in that, in the apparatus in Items 129, 131, 133, 135 137or 139, the apparatus includes a light wave composing means by which theemitted light flux from the first light source and the emitted lightflux from the second light source can be composed, and has the openinglimiting means which transmits the light flux from the second lightsource, and in the light flux from the first light source, which doesnot transmit the flux which passes through the opposite side area to theoptical axis of the diffraction pattern, between the light wavecomposing means and the optical information recording medium.

[0523] Further, the optical pickup apparatus in Item 153 ischaracterized in that, in the apparatus in Item 151, the openinglimiting means is a annular band filter, which transmits the light fluxfrom the first light source, and in the light flux of the second lightsource, which reflects or absorbs the flux which passes through theopposite side area to the optical axis of the diffraction pattern.

[0524] Further, the optical pickup apparatus in Item 154 ischaracterized in that, in the apparatus in Item 152, the openinglimiting means is a annular band filter, which transmits the light fluxfrom the second light source, and in the light flux of the first lightsource, which reflects or absorbs the flux which passes through theopposite side area to the optical axis of the diffraction pattern.

[0525] Further, the optical pickup apparatus in Item 155 ischaracterized in that, in the apparatus in Item 151, the openinglimiting means is a annular band filter, which transmits the light fluxfrom the first light source, and in the light flux of the second lightsource, which diffracts the flux which passes through the opposite sidearea to the optical axis of the diffraction pattern.

[0526] Further, the optical pickup apparatus in Item 156 ischaracterized in that, in the apparatus in Item 152, the openinglimiting means is a annular band filter, which transmits the light fluxfrom the second light source, and in the light flux of the first lightsource, which diffracts the flux which passes through the opposite sidearea to the optical axis of the diffraction pattern.

[0527] Further, the optical pickup apparatus in Item 157 ischaracterized in that, in the apparatus in any one Item of Items122-156, the light detector is in common to the first light source andthe second light source.

[0528] Further, the optical pickup apparatus in Item 158 ischaracterized in that, in the apparatus in any one Item of Items122-156, the light detector is provided separately the first lightdetector for the first light source and the second light detector forthe second light source, and these are spatially separated positionrespectively.

[0529] Further, the optical pickup apparatus in Item 159 ischaracterized in that, in the apparatus in Item 158, at lest a pair ofthe first light source and the first light detector or the second lightsource and the second light detector, is formed into a unit.

[0530] Further, the optical pickup apparatus in Item 160 ischaracterized in that, in the apparatus in Item 157, the first lightsource, the second light source, and a common light detector (a singlelight detector) are formed into a unit.

[0531] Further, the optical pickup apparatus in Item 161 ischaracterized in that, in the apparatus in Item 158, in the lightdetector, the first light detector of the first light source and thesecond light detector of the second light source are separatelyprovided, and the first light source, the second light source, the firstlight detector and the second light source are formed into a unit.

[0532] Further, the optical pickup apparatus in Item 162 ischaracterized in that, in the apparatus in any one Item of Items122-161, further the light detector to detect the transmitted light fromthe optical disk, is provided.

[0533] Further, the optical pickup apparatus in Item 163 which has: thefirst light source with the wavelength λ1; the second light source withthe wavelength λ2 (λ1≢λ2); the wave composing means by which the emittedlight flux from the first light source and the emitted light flux fromthe second light source can be composed; the diffraction optical elementhaving the diffraction pattern on at least one surface; the objectivelens by which the light flux from respective light sources are convergedonto the information recording surface of the optical informationrecording medium through the transparent substrate; and the lightdetector which receives the reflected light of the emitted light fluxfrom the first light source and the second light source, from theoptical information recording medium, the optical pickup apparatus ischaracterized in that the m-ordered diffracted ray (where, m is aninteger except 0) from the diffraction pattern of the objective lens ofthe light flux from the first light source is at least used, thereby,the first optical information recording medium in which the thickness ofthe transparent substrate is t1 is recorded and/or played back, and then-th ordered diffracted ray (where, n=m) from the diffraction pattern ofthe objective lens of the light flux from the second light source is atleast used, thereby, the second optical information recording medium inwhich the thickness of the transparent substrate is t2 (t2≢t1) isrecorded and/or played back.

[0534] Further, the optical pickup apparatus in Item 164 ischaracterized in that, in the apparatus in Item 163, the optical pickupapparatus is used under the relationship that the wavelengths λ1 and λ2of the first light source and the second light source are λ1<λ2, and thethickness t1 and t2 of the transparent substrates are t1<t2, and them-ordered and n-th ordered diffracted ray are both +first ordereddiffracted ray.

[0535] Further, the optical pickup apparatus in Item 165 ischaracterized in that, in the apparatus in Item 163, the optical pickupapparatus is used under the relationship that the wavelengths λ1 and λ2of the first light source and the second light source are λ1<λ2, and thethickness t1 and t2 of the transparent substrates are t1>t2, and them-ordered and n-th ordered diffracted ray are both −first ordereddiffracted ray.

[0536] Further, the optical pickup apparatus in Item 166 ischaracterized in that, in the apparatus in Items 163, 164 and 165, thediffraction optical element and the objective lens are integrallydriven.

[0537] Further, the optical pickup apparatus in Item 167 ischaracterized in that, in the apparatus in Items 122-166, the depth inthe optical axis of the first diffraction pattern is not more than 2 μm.

[0538] Further, the objective lens for the optical pickup apparatus inItem 168 is characterized in that it has the diffraction pattern on atleast one surface, and when the light flux of the wavelength λ1 enters,at least m-ordered diffracted ray (where, m is an integer except 0) fromthe diffraction pattern is converged onto the first light convergingposition and when the light flux of the wavelength λ2 enters, at leastn-th ordered diffracted ray (where, n=m) from the diffraction pattern isconverged onto the second light converging position which is differentfrom the first light converging position.

[0539] Further, the objective lens for the optical pickup apparatus inItem 169 is characterized in that, when the wavelengths λ1, λ2 areλ1<λ2, the first light converging position is the light convergingposition to the first optical information recording medium in which thethickness of the transparent substrate is t1, the second lightconverging position is the light converging position to the secondoptical information recording medium in which the thickness of thetransparent substrate is t2, and the thickness t1, t2 of the transparentsubstrate are t1<t2, the m-ordered and n-th ordered diffracted ray areboth +first ordered diffracted ray.

[0540] Further, the objective lens for the optical pickup apparatus inItem 170 is characterized in that, when the wavelengths λ1, λ2 areλ1<λ2, the first light converging position is the light convergingposition to the first optical information recording medium in which thethickness of the transparent substrate is t1, the second lightconverging position is the light converging position to the secondoptical information recording medium in which the thickness of thetransparent substrate is t2, and the thickness t1, t2 of the transparentsubstrate are t1>t2, the m-ordered and n-th ordered diffracted ray areboth −first ordered diffracted ray.

[0541] Further, the objective lens for the optical pickup apparatus inItem 171 is characterized in that it has the diffraction pattern on atleast one surface, and when the light flux of the wavelength λ1 enters,at least m-ordered diffracted ray (where, m is an integer except 0) fromthe diffraction pattern has the light converging position which is usedfor recording and/or reproducing the first optical information recordingmedium in which the thickness of the transparent substrate is t1, andwhen the light flux of the wavelength λ2 (where, λ2≢λ1) enters, at leastn-th ordered diffracted ray (where, n=m) from the diffraction patternhas the light converging position which is used for recording and/orreproducing the second optical information recording medium in which thethickness of the transparent substrate is t2 (where, t2≢t1).

[0542] Further, the objective lens for the optical pickup apparatus inItem 172 is characterized in that, in the objective lens in Item 171,when the wavelengths λ1, λ2 are λ1<λ2, and the thickness t1, t2 of thetransparent substrates are t1<t2, the m-ordered and n-th ordereddiffracted ray are both +first ordered diffracted ray.

[0543] Further, the objective lens for the optical pickup apparatus inItem 173 is characterized in that, in the objective lens in Item 171,when the wavelengths λ1, λ2 are λ1<λ2, and the thickness t1, t2 of thetransparent substrates are t1>t2, the m-ordered and n-th ordereddiffracted ray are both −first ordered diffracted ray.

[0544] Further, the objective lens for the optical pickup apparatus inItem 174 is characterized in that, in the objective lens in Item 172,when the necessary numerical aperture on the optical informationrecording medium side of the objective lens necessary for recordingand/or reproducing the first optical information recording medium inwhich the thickness of the transparent substrate is t1, by the firstlight source with the wavelength λ1, is NA1, and the necessary numericalaperture on the optical information recording medium side of theobjective lens necessary for recording and/or reproducing the secondoptical information recording medium in which the thickness of thetransparent substrate is t2 (t2>t1), by the second light source with thewavelength λ2 (λ2>λ1), is NA2 (NA2<NA1), the diffraction patternprovided on at least one surface of the objective lens is the rotationsymmetry to the optical axis, and +first ordered diffracted ray from thecircumference most separated from the optical axis of the diffractionpattern of the objective lens of the light flux from the first lightsource is converted into the light flux whose numerical aperture on theoptical information recording medium side is NAH1, and +first ordereddiffracted ray from the circumference nearest to the optical axis of thediffraction pattern of the objective lens of the light flux from thefirst light source is converted into the light flux whose numericalaperture on the optical information recording medium side is NAL1, andthe following conditions are satisfied: NAH1<NA1,

0≦NAL1≦NA2.

[0545] Further, the objective lens for the optical pickup apparatus inItem 175 is characterized in that, in the objective lens in Item 172,when the necessary numerical aperture on the optical informationrecording medium side of the objective lens necessary for recordingand/or reproducing the first optical information recording medium inwhich the thickness of the transparent substrate is t1, by the firstlight source with the wavelength λ1, is NA1, and the necessary numericalaperture on the optical information recording medium side of theobjective lens necessary for recording and/or reproducing the secondoptical information recording medium in which the thickness of thetransparent substrate is t2 (t2>t1), by the second light source with thewavelength λ2 (λ2>λ1), is NA2 (NA2>NA1), the diffraction patternprovided on at least one surface of the objective lens is the rotationsymmetry to the optical axis, and +first ordered diffracted ray from thecircumference most separated from the optical axis of the diffractionpattern of the objective lens of the light flux from the first lightsource is converted into the light flux whose numerical aperture on theoptical information recording medium side is NAH1, and +first ordereddiffracted ray from the circumference nearest to the optical axis of thediffraction pattern of the objective lens of the light flux from thefirst light source is converted into the light flux whose numericalaperture on the optical information recording medium side is NAL1, andthe following conditions are satisfied: NAH1<NA2,

0≦NAL1≦NA1.

[0546] Further, the objective lens for the optical pickup apparatus inItem 176 is characterized in that, in the objective lens in Item 173,when the necessary numerical aperture on the optical informationrecording medium side of the objective lens necessary for recordingand/or reproducing the first optical information recording medium inwhich the thickness of the transparent substrate is t1, by the firstlight source with the wavelength λ1, is NA1, and the necessary numericalaperture on the optical information recording medium side of theobjective lens necessary for recording and/or reproducing the secondoptical information recording medium in which the thickness of thetransparent substrate is t2 (t2<t1), by the second light source with thewavelength λ2 (λ2>λ1), is NA2 (NA2<NA1), the diffraction patternprovided on at least one surface of the objective lens is the rotationsymmetry to the optical axis, and −first ordered diffracted ray from thecircumference most separated from the optical axis of the diffractionpattern of the objective lens of the light flux from the first lightsource is converted into the light flux whose numerical aperture on theoptical information recording medium side is NAH1, and −first ordereddiffracted ray from the circumference nearest to the optical axis of thediffraction pattern of the objective lens of the light flux from thefirst light source is converted into the light flux whose numericalaperture on the optical information recording medium side is NAL1, andthe following conditions are satisfied:

NAH1<NA1,

0≦NAL1≦NA2.

[0547] Further, the objective lens for the optical pickup apparatus inItem 177 is characterized in that, in the objective lens in Item 173,when the necessary numerical aperture on the optical informationrecording medium side of the objective lens necessary for recordingand/or reproducing the first optical information recording medium inwhich the thickness of the transparent substrate is t1, by the firstlight source with the wavelength λ1, is NA1, and the necessary numericalaperture on the optical information recording medium side of theobjective lens necessary for recording and/or reproducing the secondoptical information recording medium in which the thickness of thetransparent substrate is t2 (t2<t1), by the second light source with thewavelength λ2 (λ2>λ1), is NA2 (NA2>NA1), the diffraction patternprovided on at least one surface of the objective lens is the rotationsymmetry to the optical axis, and −first ordered diffracted ray from thecircumference most separated from the optical axis of the diffractionpattern of the objective lens of the light flux from the first lightsource is converted into the light flux whose numerical aperture on theoptical information recording medium side is NAH1, and −first ordereddiffracted ray from the circumference nearest to the optical axis of thediffraction pattern of the objective lens of the light flux from thefirst light source is converted into the light flux whose numericalaperture on the optical information recording medium side is NAL1, andthe following conditions are satisfied:

NAH1<NA2,

0≦NAL1≦NA1.

[0548] Further, the objective lens for the optical pickup apparatus inItem 178 is characterized in that, in the objective lens in any one Itemof Items 168-177, the optical surface includes the diffraction patternportion and the refraction portion, and the bordered between thediffraction portion and the refraction portion includes the differencein level not less than 5 μm.

[0549] Further, the objective lens for the optical pickup apparatus inItem 179 is characterized in that, in the objective lens in any one Itemof Items 168-177, the average depth of the diffraction pattern of thediffraction portion nearest to the optical axis side is not more than 2μm.

[0550] Further, the objective lens for the optical pickup apparatus inItem 180 is characterized in that, in the objective lens in Item 179,the average depth of the diffraction pattern of the diffraction portionnearest to the optical axis side is not more than 2 μm, and the averagedepth of the diffraction pattern of the diffraction portion mostseparated from the optical axis side is not less than 2 μm.

[0551] Further, the objective lens for the optical pickup apparatus inItem 181 is characterized in that, in the objective lens in any one Itemof Items 168-180, the diffraction pattern of the optical surfaceincludes the optical axis portion.

[0552] Further, the objective lens for the optical pickup apparatus inItem 182 is characterized in that, in the objective lens in any one Itemof Items 168-180, the optical axis portion of the optical surface is notprovided with the diffraction pattern, and is the refraction surface.

[0553] Further, the objective lens for the optical pickup apparatus inItem 183 is characterized in that, in the objective lens in Items 168,169, 171, 172 or 174, when an image is formed on the informationrecording surface at a predetermined image forming magnification throughthe transparent substrate of the thickness 0.6 mm at the wavelength ofthe light source of 650 nm, it has the diffraction limit performance upto at least numerical aperture 0.6, and when an image is formed on theinformation recording surface at a predetermined image formingmagnification through the transparent substrate of the thickness 1.2 mmat the wavelength of the light source of 780 nm, it has the diffractionlimit performance up to at least numerical aperture 0.45.

[0554] Further, the objective lens for the optical pickup apparatus inItem 184 is characterized in that, in the objective lens in Item 183,the number of steps of the diffraction pattern is not more than 15.

[0555] Further, the objective lens for the optical pickup apparatus inItem 185 is characterized in that, in the objective lens in any one Itemof Items 168-184, the optical surface on which the diffraction patternis provided is a convex surface.

[0556] Further, the objective lens for the optical pickup apparatus inItem 186 is characterized in that, in the objective lens in Item 185,the refraction portion of the optical surface on which the diffractionpattern is provided, is aspherical.

[0557] Further, the objective lens for the optical pickup apparatus inItem 187 is characterized in that, in the objective lens in Item 186,the diffraction pattern includes at least one aspherical refractionportion.

[0558] Further, the objective lens for the optical pickup apparatus inItem 188 is characterized in that, in the objective lens in any one Itemof Items 168-187, the objective lens is a single lens.

[0559] Further, the objective lens for the optical pickup apparatus inItem 189 is characterized in that, in the objective lens in Item 188,the diffraction pattern is provided on only one optical surface of thesingle lens.

[0560] Further, the objective lens for the optical pickup apparatus inItem 185 is characterized in that, in the objective lens in Item 188,the diffraction pattern is provided on only one optical surface of thesingle lens, and the other optical surface is aspherical.

[0561] No-aberration parallel light is entered from the first lightsource into such that objective lens, and by using an exclusive useobjective lens which is designed such that the parallel light isconverged with no-aberration through the transparent substrate (thethickness is t1) of the first optical information recording medium, thecase where the parallel light with no-aberration enters from the secondlight source to this objective lens and passes through the transparentsubstrate (thickness t2, t2>t1) of the second optical informationrecording medium, will be considered as follows.

[0562] To the entered parallel light, when there is no substrate and thewavelength is λ1, the back focus is fB1, and when the wavelength is λ2(λ2>λ1), the back focus is fB2.

[0563] In this case, the axial chromatic aberration ΔfB is defined asΔfB=fB2−fB1 . . . (1), when the objective lens is a refraction typeaspherical single lens, ΔfB>0.

[0564] Further, when the wavelength is λ2 and the light is convergedthrough the transparent substrate of the second optical informationrecording medium, the spherical aberration when the axial focus positionis made to be the reference, does not become 0 due to the followingfactors:

[0565] (1) The spherical aberration due to the wavelength dependency ofthe refractive index of the objective lens by the change of thewavelength from λ1 to λ2.

[0566] (2) The spherical aberration generated by the difference betweenthe thickness t1 of the transparent substrate of the first opticalinformation recording medium and the thickness t2 of the transparentsubstrate of the second optical information recording medium.

[0567] (3) The spherical aberration due to the difference between therefractive index nd1 (λ1) of the transparent substrate of the firstoptical information recording medium and the refractive index nd2 (λ2)of the transparent substrate of the second optical information recordingmedium.

[0568] When the objective lens is the refraction type aspherical singlelens, the spherical aberration due to factor (1) becomes over. Thespherical aberration due to factor (2) becomes also over. Further,nd2<nd1, and the spherical aberration due to factor (3) becomes alsoover.

[0569] In the over-spherical aberration which is generated due tofactors (1)-(3), the spherical aberration due to factor (2) is almostall, and that due to factor (1) is next to it. The spherical aberrationdue to factor (3) can be almost neglected.

[0570] The above-described presupposition corresponds to the case inwhich, for example, the first optical information recording medium isthe DVD, the wavelength λ1 of the first light source is 650 nm, and thesecond optical information recording medium is the CD, the wavelength λ2of the second light source is 780 nm, and in the DVD (thickness t1=0.6mm) and the CD (thickness t2=1.2 mm), the material of the transparentsubstrate is the same, but the thickness is different.

[0571] Next, when the +first ordered diffracted ray of the diffractionpattern which is the rotation symmetry to the optical axis is viewed, asshown in FIG. 113(a), when the wavelength is longer, the diffractionangle of the +first ordered light is larger, and the +first orderedlight is more diffracted to the optical axis side, and is bent to moreunder side. That is, when the parallel light flux with no-aberrationenters from the second light source with the wavelength λ2, the +firstordered light has an action to make the axial chromatic aberration andthe spherical aberration under, as compared to the case where theparallel light flux with no-aberration enters from the first lightsource with the wavelength λ1. By using this action, the differencebetween the spherical aberration when the light is through thetransparent substrate of the second optical information recording mediumwith the wavelength λ2 and the spherical aberration when the light isthrough the transparent substrate of the first optical informationrecording medium with the wavelength λ1, can be reduced by introducingthe diffraction pattern of the rotation symmetry and using the +firstordered diffracted ray.

[0572] When the thickness t1 of the substrate of the first opticalinformation recording medium is larger than the thickness t2 of thetransparent substrate of the second optical information recordingmedium, the spherical aberration due to the factor (2) becomes under,and as shown in FIG. 12(b), by using the −first ordered diffracted rayhaving the action by which the axial chromatic aberration and thespherical aberration to be generated, become over, the aberration can bereduced.

[0573] In the present invention, in the case where the +first ordereddiffracted ray is used, when the refractive index of the material of theobjective lens at the wavelength λ1 is n(λ1), and the refractive indexof the material of the objective lens at the wavelength λ2 is n(λ2), thedepth of the diffraction pattern is λ1/{n(λ1)−1} or λ2/{n(λ2)−1}, andeven if the plastic material with comparatively small refractive indexis used, the depth is not more than 2 μm, therefore, the production ofthe objective lens to which the diffraction pattern is integrated, iseasier than the conventional hologram optical element, or the hologramtype ring lens.

[0574] Further, the optical pickup apparatus in Item 191, which has: thefirst light source with the wavelength λ1; the second light source withthe wavelength λ2 (λ1≢λ2); the objective lens having the diffractionpattern on at least one surface, and converging the light flux fromrespective light sources onto the information recording surface of theoptical information recording medium through the transparent substrate;and the light detector receiving the reflected light from the opticalinformation recording medium of the emitted light flux from the firstlight source and the second light source, the optical pickup apparatusis characterized in that, by using at least m-ordered diffracted ray(where, m is an integer except 0) from the diffraction pattern of theobjective lens of the light flux from the first light source, theoptical pickup apparatus conducts at least either one of recording andreproducing of the information to the first optical informationrecording medium in which the thickness of the transparent substrate ist1, and

[0575] by using at least n-th ordered diffracted ray (where, n=m) fromthe diffraction pattern of the objective lens of the light flux from thesecond light source, the optical pickup apparatus conducts at leasteither one of recording and reproducing of the information to the secondoptical information recording medium in which the thickness of thetransparent substrate is t2 (t2≢t1), the objective lens is made ofplastic material, the plastic material satisfies the relationship of thefollowing: when the temperature changes by ΔT (° C.), the changed amountof refractive index is defined as Δn, then,

[0576] −0.0002/° C.<Δn/ΔT<−0.00005/° C., and the first light sourcesatisfies the following: when the temperature changes by ΔT (° C.), thechanged amount of the emission wavelength is defined as Δλ1 (nm), then,0.05 nm/° C.<Δλ1/ΔT<0.5 nm/° C.

[0577] According to Item 191, the characteristic variation of theoptical pickup apparatus due to the temperature change of the refractiveindex in the objective lens of plastic and the characteristic variationof the optical pickup apparatus due to the temperature change of thewavelength in the light source are acted toward the direction to becancelled with each other, and the compensation effect can be obtained,thereby, the pick-up apparatus which is very strong to the temperaturechange, can be obtained.

[0578] Further, the optical pickup apparatus in Item 192 which isprovided with: the first light source with the wavelength λ1; the secondlight source with the wavelength λ2 (λ1≢λ2); the objective lens havingthe diffraction pattern on at least one surface, and converging thelight flux from respective light sources onto the information recordingsurface of the optical information recording medium through thetransparent substrate; and the light detector receiving the reflectedlight from the optical information recording medium of the emitted lightflux from the first light source and the second light source, theoptical pickup apparatus is characterized in that, by using at leastm-ordered diffracted ray (where, m is an integer except 0) from thediffraction pattern of the objective lens of the light flux from thefirst light source, the optical pickup apparatus conducts at leasteither one of recording and reproducing of the information to the firstoptical information recording medium in which the thickness of thetransparent substrate is t1, and by using at least n-th ordereddiffracted ray (where, n=m) from the diffraction pattern of theobjective lens of the light flux from the second light source, theoptical pickup apparatus conducts at least either one of recording andreproducing of the information to the second optical informationrecording medium in which the thickness of the transparent substrate ist2 (t2≢t1), and the wavelengths λ1, λ2, and the thickness of thetransparent substrates t1 and t2 have the relationship λ2>λ1, t2>t1, andin the case where the necessary numerical aperture on the opticalinformation recording medium side of the objective lens necessary forrecording and/or reproducing the first optical information recordingmedium by the first light source is NA1, the focal distance of theobjective lens at the wavelength λ1 (mm) is f1 (mm), and theenvironmental temperature change is ΔT(° C.), when the changed amount ofthe third-ordered spherical aberration component of the wave frontaberration of the light flux converged onto the information recordingsurface of the first information recording medium is ΔWSA3 (λ1 rms), thefollowing relationship is satisfied:

0.2×10⁻⁶ /° C.<ΔWSA3·λ1/{f·(NA1)⁴ ·ΔT}<2.2×10⁻⁶ /° C.

[0579] According to Item 192, when the value of the objective term isnot more than the upper limit, even if the environmental temperaturechanges, the characteristic as the pick-up apparatus can be easilymaintained, and when the value of the objective term is not less thanthe lower limit, even when only the wavelength changes, thecharacteristic as the pick-up apparatus can be easily maintained.

[0580] Further, the optical pickup apparatus in Item 193 ischaracterized in that, in Items 191 or 192, at least one collimator isincluded between the first light source and the objective lens, and thesecond light source and the objective lens, and the light flux enteringfrom the first light source to the objective lens and the light fluxentering from the second light source to the objective lens, arerespectively almost parallel light.

[0581] Further, the optical pickup apparatus in Item 194 ischaracterized in that, in Items 191, 192 or 193, t1 is 0.55 mm-0.65 mm,t2 is 1.1 mm-1.3 mm, λ1 is 630 nm-670 nm, and λ2 is 760 nm-820 nm.

[0582] Further, the optical pickup apparatus in Item 192 which isprovided with: the first light source with the wavelength λ1; the secondlight source with the wavelength λ2 (λ1≢λ2); the objective lens havingthe diffraction pattern on at least one surface, and converging thelight flux from respective light sources onto the information recordingsurface of the optical information recording medium through thetransparent substrate; and the light detector receiving the reflectedlight from the optical information recording medium of the emitted lightflux from the first light source and the second light source, theoptical pickup apparatus is characterized in that, by using at leastm-ordered diffracted ray (where, m is an integer except 0) from thediffraction pattern of the objective lens of the light flux from thefirst light source, the optical pickup apparatus conducts at leasteither one of recording or reproducing of the information to the firstoptical information recording medium in which the thickness of thetransparent substrate is t1, and by using at least n-th ordereddiffracted ray (where, n=m) from the diffraction pattern of theobjective lens of the light flux from the second light source, theoptical pickup apparatus conducts at least either one of recording orreproducing of the information to the second optical informationrecording medium in which the thickness of the transparent substrate ist2 (t2≢t1), and has a correction means for compensating the divergencedegree of the light flux entering from at least one light source of thefirst and the second light sources into the objective lens.

[0583] According to Item 195, by compensating the divergence degree ofthe light flux entering into the objective lens, the third-orderedspherical aberration of the whole optical system including the objectivelens can be corrected according to the design value.

[0584] Further, the optical pickup apparatus in Item 196 which, in Item195, includes at least a collimator between the first light source andthe objective lens, and the second light source and the objective lens,and the optical pickup apparatus in Item 197 is characterized in thatthe correction of the divergence degree by the correction means isconducted by changing the distance between the first and/or the secondlight source and at least one collimator. The correction of thedivergence degree by the correction means is characterized in that it isconducted by changing the distance between the first and/or the secondlight source and at least one collimator. By changing the distancebetween the light source and the collimator, the divergence degree ofthe light flux entering from at least one light source into theobjective lens can be corrected.

[0585] Further, the optical pickup apparatus in Item 192 which isprovided with: the first light source with the wavelength λ1; the secondlight source with the wavelength λ2 (λ1≢λ2); the objective lens havingthe diffraction pattern on at least one surface, and converging thelight flux from respective light sources onto the information recordingsurface of the optical information recording medium through thetransparent substrate; and the light detector receiving the reflectedlight from the optical information recording medium of the emitted lightflux from the first light source and the second light source, theoptical pickup apparatus is characterized in that, by using at leastm-ordered diffracted ray (where, m is an integer except 0) from thediffraction pattern of the objective lens of the light flux from thefirst light source, the optical pickup apparatus conducts at leasteither one of recording or reproducing of the information to the firstoptical information recording medium in which the thickness of thetransparent substrate is t1, and by using at least n-th ordereddiffracted ray (where, n=m) from the diffraction pattern of theobjective lens of the light flux from the second light source, theoptical pickup apparatus conducts at least either one of recording orreproducing of the information to the second optical informationrecording medium in which the thickness of the transparent substrate ist2 (t2≢t1), and the wave front aberration on the image formation surfaceis not more than 0.07 λrms in the maximum numerical aperture on theimage side of the objective lens, to each of the light having 2different wavelengths (λ) outputted from the first and the second lightsources.

[0586] According to Item 198, there is no flare on each informationrecording surface and the light detector in recording and/or reproducingof the first and the second information recording medium, thereby, thecharacteristic of the optical pickup apparatus becomes excellent.

[0587] Further, the optical pickup apparatus in Item 199 ischaracterized in that, in any one Item of Items 122-156, and 198, thefirst light source and the second light source are formed into a unit,and the light detector is in common to the first light source and thesecond light source.

[0588] Hereinafter, referring to the drawings, detailed embodiments ofthe present invention will be described.

[0589] An optical system of the first embodiment of the presentinvention is basically a 2-sided aspherical single lens, and diffractionannular bands (ring zonal diffraction surface) are provided on oneaspherical surface. Generally, in the aspherical refractive surface,when the spherical aberration is corrected to a certain dominantwavelength light, to the wavelength light whose wavelength is shorterthan that of the dominant wavelength light, the spherical aberrationbecomes under (insufficient correction). Reversely, in a diffractionlens which is a lens having the diffraction surface, when the sphericalaberration is corrected by the dominant wavelength light, the sphericalaberration can be over (excessive correction) at the wavelength which isshorter than that of the dominant wavelength light. Accordingly, when anaspherical coefficient of the aspherical surface lens by the refraction,and an coefficient of the phase difference function of the diffractionlens are properly selected and the refraction power and diffractionpower are combined, the spherical aberration can be finely corrected byboth of 2 different wavelength light.

[0590] Further, generally, the pitch of the diffraction annular band isdefined by using the phase difference function or the optical pathdifference function, which will be detailed in a later example.Concretely, the phase difference function ΦB is expressed in thefollowing [Equation 1] in radian unit, and the optical path differencefunction Φb is expressed by (Equation 2] in mm unit. $\begin{matrix}{\Phi_{B} = {\sum\limits_{i - 1}^{\infty}\quad {B_{2\quad i}h_{21}}}} & \lbrack {{Equation}\quad 1} \rbrack \\{\Phi_{b} = {\sum\limits_{i = 1}^{\infty}\quad {b_{2\quad i}h_{2i}}}} & \lbrack {{Equation}\quad 2} \rbrack\end{matrix}$

[0591] These 2 expression methods are, although the unit is differentfrom each other, equal to each other in a meaning that these express thepitch of the diffraction annular band. That is, to the dominantwavelength λ (mm unit), when the coefficient B of the phase differencefunction is multiplied by λ/2π, it can be converted into the coefficientb of the optical path difference function, or reversely, when thecoefficient b of the optical path difference function is multiplied by2π/λ, it can be converted into the coefficient B of the phase differencefunction.

[0592] Herein, for a simple explanation, the diffraction lens which usesfirst ordered diffracted ray, will be described. In the case of theoptical path difference function, the annular band is notched for eachtime when the function value exceeds the integer times of the dominantwavelength λ, and in the case of the phase difference function, theannular band is notched for each time when the function value exceedsthe integer times of 2π.

[0593] For example, a lens in which the diffraction annular band isnotched on the side of 2-sided cylindrical material having no refractionpower, is considered, and when the dominant wavelength is 0.5 μm=0.0005mm, the second power coefficient (second power term) of the optical pathdifference function is −0.05 (when converted into the second powercoefficient of the phase difference function, it is −628.3), and otherpower coefficients are all zero, the diameter of the first annular bandis h=0.1 mm, and the diameter of the second annular band is h=0.141 mm.Further, as for the focal distance f of this diffraction lens, to secondpower coefficient b2 of the optical path difference function b2=−0.05,f=−1/(2·b2)=10 mm is known.

[0594] Herein, in the case where the above definition is used as thebase, when the second power coefficient of the phase difference functionor the optical path difference function is a value of not zero, thechromatic aberration near the optical axis, so-called in the paraxialarea, can be corrected. Further, when coefficients other than the secondpower coefficient of the phase difference function or the optical pathdifference function, for example, fourth power coefficient, sixth powercoefficient, eighth power coefficient, tenth power coefficients, etc.,are made to a value of not zero, the spherical aberration between 2wavelengths can be controlled. Incidentally, herein, “control” meansthat the difference of spherical aberration between 2 wavelengths can bemade very small, and the difference which is necessary for the opticalspecification can also be provided.

[0595] As the concrete application of the above description, whencollimate light (parallel light) from 2 light sources having differentwavelengths are made to simultaneously enter into the objective lens,and to image-form on the optical disk, it is preferable that, initially,the paraxial axial chromatic aberration is corrected by using the secondpower coefficient of the phase difference function or the optical pathdifference function, and further, the difference between 2 wavelengthsof the spherical aberration is made smaller so that it is within theallowable value, by using the coefficients of the fourth power andsubsequent powers of the phase difference function or the optical pathdifference function.

[0596] Further, as another example, the specification in which oneobjective lens is used for the light from 2 light sources havingdifferent wavelengths, and for the light of one wavelength, theaberration is corrected for the disk having the thickness (the thicknessof the transparent substrate) of t1, and for the light of the otherwavelength, the aberration is corrected for the disk having thethickness of t2, will be considered below. In this case, when thecoefficients subsequent to fourth power of the phase difference functionor the optical path difference function are mainly used, the differenceof the spherical aberration between 2 wavelengths is provided, and thespherical aberration can be made to be corrected by respectivewavelengths for respective thickness. Further, in both cases, for therefraction surface, the aspherical surface is better than the sphericalsurface for easy aberration correction between 2 wavelengths.

[0597] The above-described aspherical refraction surface has respectivedifferent refraction powers for different wavelengths, and has differentlight converging points, therefore, respective light converging pointscan correspond to optical disks having respective substrate thickness.In this case, the shorter wavelength of the light source is not morethan 700 nm, the longer wavelength of the light source is not less than600 nm, and it is preferable that the difference of the wavelengths isnot less then 80 nm. Further, it is more preferable that the differenceof the wavelengths is not more than 400 nm, and further preferably, thedifference of the wavelengths is not less than 100 nm, and not more than200 nm. It is desirable that the diffraction surface has, to the lighthaving 2 different wavelengths, the maximum diffraction efficiency atalmost the middle wavelength thereof, however, the diffraction surfacemay have the maximum diffraction efficiency at either one wavelength.

[0598] By using the same action as the correction of the sphericalaberration, the diffraction annular band lens is provided on the opticalsurface, and for each of the light sources with 2 different wavelengths,the axial chromatic aberration can be corrected by a certain one sameordereded diffracted ray. That is, the axial chromatic aberration forthe light of the light sources with 2 different wavelengths can becorrected within the range of ±λ/(2NA2). Where, λ is the longerwavelength of 2 wavelengths, and NA is an image side numerical aperturecorresponding to the longer wavelength.

[0599] Further, when the difference of wavelengths of the light sourceswith 2 different wavelengths is not less than 80 nm, and Abbe's numberof the glass material of the objective lens is νd, the followingconditional expression

νd>50  (1)

[0600] is desirably satisfied. The conditional expression (1) is acondition to reduce the second ordered spectrum when the axial chromaticaberration is corrected for the light sources with 2 differentwavelengths.

[0601] Next, when the diffraction surface is provided on one surface ofa thin single lens, the whole single lens is considered as thecomposition of the refraction lens as a base from which the diffractionrelief is taken off and the diffraction surface, and the chromaticaberration of this composition lens will be considered below. Theachromatic condition by a certain wavelength λx and the wavelength λy(λx<λy) is as follow.

[0602] fR·νR+fD·νD=0 Where, fR, fD : a focal distance of respectiverefraction lens and diffraction surface, and νR, νD : Abbe's number ofrespective refraction lens and diffraction surface, and are determinedby the following expressions:

νR=(n0−1)/(nx−ny)

νD=λ0/(λx−λy)

[0603] Where, n0: the refractive index at the reference wavelength, andλ0: the reference wavelength.

[0604] In this case, the chromatic aberration δf to a certain wavelengthλz is expressed by the following equation:

δf=f(θR−θD)/(νR−νD)  (2)

[0605] Where, θR, θD: respective partial variance ratios of therefraction lens and the diffraction surface, and are determined by thefollowing equations.

θR=(nx−nz)/(nx−ny)

θD=(λx−λz)/(λx−λy)

[0606] where, nz: the refractive index at the wavelength λz.

[0607] As an example, when λ0=λx=635 nm, λy=780 nm, λz=650 nm, and theglass material of the refraction lens as the base is BSC7 (νd=64.2) madeby Hoya Co., then, λR=134.5, λD=−4.38, θR=0.128, θD=0.103, are obtained,and then, δf=0.18×10⁻³f is obtained.

[0608] Further, when the glass material of the refraction lens as thebase is changed to E−FD1(νd=29.5) made by Hoya Co., then, νR=70.5,θR=0.136 are obtained, and then, δf=0.44×10⁻³f is obtained.

[0609] As described above, in Equation (2), in the denominator of theright side (νR−νD), because |νD| is very smaller than |νR|, the changeof Abbe's number νR of the refraction lens is dominant over the changeof the chromatic aberration δf by replacing the glass material of therefraction lens. On the one hand, θR and θD are determined only by thewavelength, and the contribution of the change of the numerator (θR−θD)of the right side is smaller than that of the denominator (νR−νD) of theright side.

[0610] According to the above description, in the lens having thediffraction surface, in ordered to suppress the secondary spectrum δfsmall, it is understood that the selection of the material having thelarger Abbe's number νR is effective for the material of the refractionlens. The conditional expression (1) shows the effective limit tosuppress the secondary spectrum so as to cope with the change ofwavelength of the light source.

[0611] Further, in the case where the achromatic processing is conductedwithout using the diffraction surface and by adhering the refractionlenses of 2 kinds of materials, when, for respective materials,θR=a+b·νR+ΔθR (a, b are constant) is expressed, if ΔθR is small, andthere is no abnormal dispersibility, the secondary spectrum δf does notdepend on Abbe's number νR of 2 refraction lenses. Accordingly, it isunderstood that the expression (1) is a condition specific to thediffraction optical system.

[0612] In ordered to easily produce the diffractive lens in the presentembodiment, it is preferable that the objective lens is composed ofplastic material. AS the plastic material to satisfy the conditionalexpression (1), acrylic system, polyolefine system plastic materials areused, however, from the view point of humidity resistance and heatresistance, the polyolefine system is preferable.

[0613] Next, the objective lens of the second embodiment of the presentinvention and the structure of the optical pickup apparatus providedwith the objective lens will be concretely described.

[0614] In FIG. 48, the schematic structural view of the optical pickupapparatus of the present embodiment will be shown. The optical disks 20which are optical information recording media onto which or from whichthe information is recorded and/or played back by the optical pickupapparatus, are 3 types of disks which are the first optical disk (forexample, a DVD) whose transparent substrate thickness is t1 and thesecond optical disk (for example, a blue laser use next-generation highdensity optical disk), and the third optical disk (for example, a CD)whose transparent substrate thickness is t2 different from t1, andhereinafter, these disks will be described as optical disks 20. Herein,the transparent substrate thickness t1=0.6 mm, and t2=1.2 mm.

[0615] The optical pickup apparatus shown in the drawing has, as thelight sources, the first semiconductor laser 11 (wavelength λ₁=610nm-670 nm) which is the first light source, the blue laser 12(wavelength λ₂=400 nm-440 nm) which is the second light source, and thesecond semiconductor laser 13 (wavelength λ₃=740 nm-870 nm) which is thethird light source, and has the objective lens 1 as a part of theoptical system. The first light source, second light source and thirdlight source are selectively used corresponding to the optical disks torecord and/or reproduce the information.

[0616] The diverging light flux emitted from the first semiconductorlaser 11, the blue laser 12 or the second semiconductor laser 13transmits through the transparent substrate 21 of the optical disk 20through the beam splitter 19 and the diaphragm 3, and is converged ontorespective information recording surfaces 22 by the objective lens 1,and forms spots.

[0617] The incident light from each laser becomes modulated reflectedlight by the information pit on the information recording surface 22,and enters into the common light detector 30 through the beam splitter18 and a toric lens 29, and by using its output signal, the read-outsignal of the information recorded on the optical disk 20, the focusingdetection signal and the track detection signal are obtained.

[0618] Further, the diaphragm 3 provided in the optical path is, in thisexample, a diaphragm having the fixed numeral aperture (NA 0.65), andsuperfluous mechanism is not needed, therefore, cost reduction can berealized. Incidentally, when the third disk is recorded and/or playedback, the numeral aperture of the diaphragm 3 may be changeable so thatthe unnecessary light (more than NA 0.45) can be removed.

[0619] When the zonal filter is integrally formed on the optical surfaceof the objective lens 1 so that the light flux of a part of the outsideof the practically used aperture is shielded, the flare light of theoutside of the practically used aperture can also be easily removed bythe low cost structure.

[0620] When a definite conjugation type optical system is used as in thepresent embodiment, it is necessary that the relationship between thelight source and light converging optical system is kept constant tomaintain the light converging performance, and it is desirable that asthe movement for focusing or tracking, the light sources 11, 12 and 13and the objective lens 1 are moved as one unit.

[0621] Next, the objective lens and the structure of the optical pickupapparatus including the objective lens of the third embodiment of thepresent invention, will be concretely described.

[0622] In FIG. 49, the schematic structural view of the optical pickupapparatus of the present embodiment will be shown. The optical pickupapparatus shown in FIG. 49 is an example in which the laser/detectorintegration unit 40 into which the laser, light detector, and hologramare structured as a unit, is used, and the same components as in FIG. 48are shown by the same numeral codes. In this optical pickup apparatus,the first semiconductor laser 11, blue laser 12, the first lightdetection means 31, the second light detection means 32 and the hologrambeam splitter 23 are structured into a unit as the laser/detectorintegration unit 40.

[0623] When the first optical disk is played back, the light fluxemitted from the first semiconductor laser 11 transmits trough thehologram beam splitter 23, and is stopped down by the diaphragm 3, andconverged onto the information recording surface 22 by the objectivelens 1 through the transparent substrate 21 of the first optical disk20. Then, the light flux modulated by the information pit and reflectedon the information recording surface 22 is diffracted again on thesurface of the disk side of the hologram beam splitter 23 through theobjective lens 1 and the diaphragm 3, and enters onto the first lightdetector 31 corresponding to the first semiconductor laser 11. Then, byusing the output signal of the first light detector 31, the read-outsignal of the information recorded on the first optical disk 20,focusing detection signal, and track detection signal are obtained.

[0624] When the second optical disk is played back, the light fluxemitted from the blue laser 12 is diffracted by the surface on the laserside of the hologram beam splitter 23, and advances on the same opticalpath as the light flux from the first semiconductor laser 11. That is,the surface on the semiconductor laser side of the hologram beamsplitter 23 functions as the light composition means. Further, thislight flux is converged onto the information recording surface 22through the diaphragm 3, objective lens 1, and through the transparentsubstrate 21 of the second optical disk 20. Then, the light fluxmodulated by the information pit and reflected on the informationrecording surface 22, is diffracted by the surface on the disk side ofthe hologram beam splitter 23 through the objective lens 1 and thediaphragm 3, and enters onto the second light detector 32 correspondingto the blue laser 12. Then, by using the output signal of the secondlight detector 32, the read-out signal of the information recorded onthe second optical disk 20, focusing detection signal, and trackdetection signal are obtained.

[0625] Further, when the third optical disk is played back, thelaser/detector integration unit 41, which is structured into a unit bythe second semiconductor laser 13, the third light detecting means 33,and the hologram beam splitter 24, is used. The light flux emitted fromthe second semiconductor laser 13 transmits through the hologram beamsplitter 24, and is reflected by the beam splitter 19 which is thecomposition means of the emitted light, stopped down by the diaphragm 3,and converged onto the information recording surface 22 through thetransparent substrate 21 of the optical disk 20 by the objective lens 1.Then, the light flux modulated by the information pit and reflected onthe information recording surface 22 is diffracted by the hologram beamsplitter 24 again through the objective lens 1, the diaphragm 3, and thebeam splitter 19, and entered onto the light detector 33. Then, by usingthe output signal of the third light detector 33, the read-out signal ofthe information recorded on the third optical disk 20, focusingdetection signal, and track detection signal are obtained.

[0626] In the optical pickup apparatus in the second and thirdembodiments, the zonal diffraction surface concentric with the opticalaxis 4 is structured on the aspherical refraction surface of theobjective lens 1. Generally, in the case where the objective lens isstructured only by the aspherical refraction surface, when the sphericalaberration is corrected for a certain wavelength λa, the sphericalaberration becomes under for the wavelength λb shorter than λa. On theone hand, in the case where the diffraction surface is used, when thespherical aberration is corrected for a certain wavelength λa, thespherical aberration becomes over for the wavelength λb shorter than λa.Accordingly, when the aspherical surface optical design by therefraction surface, and the coefficient of the phase difference functionof the diffraction surface is appropriately selected, and the refractionpower and the diffraction power are combined, the spherical aberrationbetween different wavelengths can be corrected. Further, on theaspherical refraction surface, when the wavelength is different, therefraction power also changes, and the light converging position is alsodifferent. Accordingly, when the aspherical refraction surface isappropriately designed, the light with the different wavelength can alsobe converged onto the information recording surface 22 of eachtransparent substrate 21.

[0627] Further, in the objective lens 1 of the second and thirdembodiments, when the phase difference function of the asphericalrefraction surface and the ring zonal diffraction surface isappropriately designed, the spherical aberration generated by thedifference of the thickness of the transparent substrates 21 of theoptical disks 20 is corrected for each light flux emitted from the firstsemiconductor laser 11, blue laser 12, or the second semiconductor laser13. Further, on the ring zonal diffraction surface, when thecoefficients of 4th power and subsequent terms of the power series areused as the phase difference function expressing the position of theannular band, the chromatic aberration of the spherical aberration canbe corrected. Incidentally, as for the third optical disk (CD), theaperture in the practical use is NA 0.45, and on the third optical disk,the spherical aberration is corrected within NA 0.45, and the sphericalaberration in the outside area of NA 0.45 is made the flare. By thesecorrections, for each optical disk 20, the aberration of the lightconverging spot on the image recording surface 22 becomes almost thesame degree as the diffraction limit (0.07 λrms) or lower than it.

[0628] Above-described optical pickup apparatus in the second and thirdembodiments can be mounted in a recording apparatus for the audio and/orimage, or a reproducing apparatus for the audio and/or image of acompatible player or drive, or an AV device in which these areassembled, personal computer, and other information terminals, forarbitrary different 2 or more of, that is, for a plurality of opticalinformation recording media, such as, for example, a CD, CD-R, CD-RW,CD-Video, CD-ROM, DVD, DVD-ROM, DVD-RAM, DVD-R, DVD-RW, MD, etc.

[0629] Next, the structure of the objective lens and the optical pickupapparatus including it of the fourth embodiment of the present inventionwill be concretely described.

[0630]FIG. 67 is a schematic structural view of the optical pickupapparatus 10 of the present embodiment. In FIG. 67, the common membersto those in the second and the third embodiments are sometimes denotedby the same numeral code. In FIG. 67, the optical pickup apparatus 10records/plays back a plurality of optical disks 20 which are opticalinformation recording media. Hereinafter, the plurality of optical disks20 will be described as the first optical disk (DVD) whose transparentsubstrate thickness is t1, and the second optical disk (blue laser usenext-generation high density optical disk), and the third optical disk(CD) having the thickness t2 of the transparent substrate, which isdifferent from t1. Herein, the thickness of the transparent substratet1=0.6 mm, t2=1.2 mm.

[0631] The optical pickup apparatus 10 has, as the light source, thefirst semiconductor laser 11 (the wavelength λ₁=610 nm-670 nm) which isthe first light source, the blue laser 12 (the wavelength λ₂=400 nm-440nm) which is the second light source, and the second semiconductor laser13 (the wavelength λ₃=740 nm-870 nm) which is the third light source.These first light source, second light source, and third light sourceare exclusively used corresponding to the optical disk to berecorded/played back.

[0632] The light converging optical system 5 is a means for convergingthe light flux emitted from the first semiconductor laser 11, blue laser12 and second semiconductor laser 13 onto the information recordingsurface 22 through the transparent substrate 21 of the optical disk 20and for forming the spot. In the present example, the light convergingoptical system 5 has the collimator lens 2 to convert the light fluxemitted from the light source into the parallel light (may be almostparallel), and the objective lens 1 to converge the light flux convertedto the parallel light by the collimator lens 2.

[0633] On both surfaces of the objective lens 1, the ring zonaldiffraction surfaces which are concentric with the optical axis 4, arestructured. Generally, in the case where the light converging opticalsystem 5 is structured by only the aspherical refraction surface, whenthe spherical aberration is corrected for a certain wavelength λa, thespherical aberration becomes under for the wavelength λb shorter thanλa. On the one hand, in the case where the refraction surface is used,when the spherical aberration is corrected for a certain wavelength λa,the spherical aberration becomes over for the wavelength λb shorter thanλa. Accordingly, when the aspherical surface optical design by therefraction surface, and the coefficient of the phase difference functionof the diffraction surface is appropriately selected, and the refractionpower and the diffraction power are combined, the spherical aberrationbetween different wavelengths can be corrected. Further, on theaspherical refraction surface, when the wavelength is different, therefraction power also changes, and the light converging position is alsodifferent. Accordingly, when the aspherical refraction surface isappropriately designed, the light with the different wavelength can alsobe converged onto the information recording surface 22 of eachtransparent substrate 21.

[0634] On the above-described ring zonal diffraction surface, theaberration is corrected by using the first ordered diffracted ray foreach light flux emitted from the first semiconductor laser 11, the bluelaser 12 or the second semiconductor laser 13. When the same ordereddiffracted ray corresponds to the light flux, the loss of the lightamount is smaller than the case where the different ordered diffractedray corresponds to the light flux, and further, when the first ordereddiffracted ray is used, the loss of the light amount is smaller than thecase where the higher ordered diffracted ray corresponds to the lightflux. Accordingly, the objective lens 1 of the present embodiment iseffective in the optical pickup apparatus to record the information ontothe optical disk such as the DVD-RAM, into which the high densityinformation is recorded. Further, the diffracted surface is desirable inthat, for the light with 3 different wavelengths, the diffractionefficiency is maximum at the middle wavelength thereof, however, it mayhave the maximum diffraction efficiency at the wavelengths on the bothends thereof.

[0635] Further, when the phase difference function of the asphericalsurface refraction surface and the ring zonal diffraction surface isappropriately designed, the spherical aberration generated by thedifference of the thickness of the transparent substrate 21 of theoptical disk 20 is corrected for each light flux emitted from the firstsemiconductor laser 11, blue laser 12 and second semiconductor laser 13.Further, in the phase difference function to show the position of theannular band formed on the objective lens 1, when the coefficient of thefourth power term and subsequent terms in the power series is used, thechromatic aberration of the spherical aberration can be corrected.Incidentally, as for the third optical disk (CD), the aperture in thepractical use is NA 0.45, and the spherical aberration is correctedwithin NA 0.45, and the spherical aberration in the outside range of NA0.45 is made the flare. The light flux passing through an area within NA0.45 forms the light spot on the information recording surface, and theflare light passing the outside of NA 0.45 passes through a distant areafrom the light spot on the information recording surface so that it doesnot affect badly. According to these corrections, for each optical disk20, the aberration of the light converging spot on the informationrecording surface becomes almost the same degree as the diffractionlimit (0.07 λrms) or lower than that.

[0636] In the present embodiment, the diaphragm 3 provided in theoptical path is a diaphragm having the fixed numeral aperture (NA 0.65),and superfluous mechanism is not needed, therefore, cost reduction canbe realized. Incidentally, when the third disk is recorded and/or playedback, the numeral aperture of the diaphragm 3 may be changeable so thatthe unnecessary light (more than NA 0.45) can be removed. Further, thebeam splitter 67 is used for adjusting the optical axis of each laserlight. The light detector (not shown) may be, as well known,respectively provided for each of light sources, or one light detectormay receive the reflected light corresponding to 3 light sources 11, 12and 13.

[0637] Next, the objective lens of the fifth embodiment of the presentinvention will be described.

[0638] In the present embodiment, on the ring zonal diffraction surface,only a point that the phase difference function to express the positionof the annular band uses the coefficient of second power term in thepower series, is different from the objective lens in the abovedescribed fourth embodiment, and thereby, the axial chromatic aberrationcan also be corrected. Further, according to the objective lens of thepresent embodiment, in the same manner as the fourth embodiment, foreach optical disk 20, the aberration of the light converging spot on theinformation recording surface 22 becomes almost the same degree as thediffraction limit (0.07 λrms) or smaller than that.

[0639] Next, the optical pickup apparatus of the sixth embodiment of thepresent invention will be described.

[0640] In the optical pickup apparatus of the present embodiment, forthe first optical disk (for example, DVD) and the second optical disk(for example, blue laser use next-generation high density optical disk),the light flux emitted from the light source is made into the parallellight by the coupling lens, and for the third optical disk (for example,CD), the light flux emitted from the light source is made into thedivergent light by the coupling lens, and these are respectivelyconverged by the objective lens. The thickness of the transparentsubstrates 21 of the first and the second optical disks is 0.6 mm, andthe thickness of the transparent substrate 21 of the third optical diskis 1.2 mm.

[0641] In the present embodiment, both of the spherical aberration ofthe first optical disk and the second optical disk are corrected withinthe diffraction limit by the effect of the diffraction surface, and forthe third optical disk, the spherical aberration generated by thethickness of the disk larger than that of the first and second opticaldisks is mainly cancelled by the spherical aberration generated byentrance of the divergent light flux into the objective lens, and thespherical aberration at the numerical aperture lower than apredetermined numerical aperture NA necessary for recording/reproducingof the third optical disk, for example, NA 0.5, or NA 0.45, is made tobe corrected within the diffraction limit.

[0642] Accordingly, when, for the optical information recording mediacorresponding to each wavelength of λ₁, λ₂, λ₃ (λ₁<λ₂<λ₃), predeterminednumerical apertures necessary for recording/reproducing them are NA1,NA2 and NA3, for respective wavelengths, RMS of the wave frontaberration can be corrected to a lower value than 0.07 λ₁ within therange of NA1, to a lower value than 0.07 λ₂ within the range of NA2, andto a lower value than 0.07 λ₃ within the range of NA3.

[0643] Further, for the third optical disk, it is not preferable thatthe beam spot diameter becomes too small by the light flux of thenumerical aperture NA larger than a predetermined numerical aperture NA.Accordingly, it is preferable that, in the same manner as the fourthembodiment, in the numerical aperture larger than a necessary numericalaperture, the spherical aberration is made the flare.

[0644] The above-described optical pickup apparatus having 3 lightsources with different wavelength light in the fourth—the sixthembodiments, can be mounted in a recording apparatus for the audioand/or image, or a reproducing apparatus for the audio and/or image of acompatible player or drive, or an AV device in which these areassembled, personal computer, and other information terminals, forarbitrary different 2 or more of, that is, for a plurality of opticalinformation recording media, such as, for example, a CD, CD-R, CD-RW,CD-Video, CD-ROM, DVD, DVD-ROM, DVD-RAM, DVD-R, DVD-RW, MD, etc.

EXAMPLE

[0645] Examples of the objective lens of the present invention will bedescribed below.

Examples 1-8

[0646] The objective lens in Examples 1-8 is concrete examples of theobjective lens according to the first embodiment, and has the asphericalshape expressed by the following [Equation 3] on the refraction surface.$\begin{matrix}{Z = {\frac{h_{2}/R_{0}}{1 + \sqrt{1 - {( {1 + \kappa} )( {h/R_{0}} )_{2}}}} + {\sum\limits_{i = 2}^{\infty}\quad {A_{2\quad i}h_{2i}}}}} & \lbrack {{Equation}\quad 3} \rbrack\end{matrix}$

[0647] Where, Z is an axis in the optical axis direction, h is an axisin the perpendicular direction to the optical axis (height from theoptical axis: an advance direction of the light is positive), R0 is theparaxial radius of curvature, κ is a conical coefficient, A is anaspherical coefficient, and 2i is an exponent of the aspherical surface.Further, in Examples 1-3, 6-8, the diffraction surface is expressed by[Equation 1] as the phase difference function ΦB in a unit of radian,and in the same manner, in Examples 4 and 5, the diffraction surface isexpressed by [Equation 2] as the optical path difference function Φb ina unit of mm. $\begin{matrix}{\Phi_{B} = {\sum\limits_{i - 1}^{\infty}\quad {B_{2\quad i}h_{21}}}} & \lbrack {{Equation}\quad 1} \rbrack\end{matrix}$

$\begin{matrix}{\Phi_{b} = {\sum\limits_{i = 1}^{\infty}\quad {b_{2\quad i}h_{2i}}}} & \lbrack {{Equation}\quad 2} \rbrack\end{matrix}$

Example 1

[0648] A view of the optical path of the diffraction optical lens (theobjective lens having the diffraction surface) which is the objectivelens in Example 1, is shown in FIG. 1. A view of the sphericalaberration up to the numerical aperture 0.60 to λ=635 nm for thediffraction optical lens in Example 1, is shown in FIG. 2. Further,views of the spherical aberration up to the numerical apertures 0.45 and0.60 to the wavelength λ=780 nm for the diffraction optical lens inExample 1, are shown in FIG. 3 and FIG. 4. Incidentally, although thediffractive lens shown in FIG. 1 is provided blazed type coaxial annularbands on its entire lens surface, a relief shape of the diffractivesection is omitted in this figure. Also, in the following figures, therelief shape of the diffractive section is omitted.

[0649] According to the diffraction optical lens in Example 1, as shownin FIG. 2, at all apertures up to NA 0.60 to the wavelength λ=635 nm,there is almost no aberration. Further, as shown in FIG. 3, to thewavelength λ=780 nm, up to NA 0.45 which is a range of practical use,there is almost no aberration. In the portion of NA 0.45-0.60 of theoutside of it, as shown in FIG. 4, the spherical aberration is largelyunder, and is made the flare. According to this, an appropriate spotdiameter can be obtained.

[0650] Views of the wave front aberration to the wavelengths λ=635 nmand λ=780 nm of the diffraction lens in Example 1 are respectively shownin FIG. 5 and FIG. 6. As can be seen from these views, according to thediffraction optical lens in Example 1, to any wavelength, there is noaberration on the optical axis, and even in the case of the image height0.03, the aberration is on the level of almost no aberration in thepractical use.

[0651] Lens data of Example 1 will be shown as follows. In [Table 1], Ris the radius of curvature, d is the space between surfaces, n is therefractive index at the main wavelength, and ν is Abbe's number.

Example 1

[0652] When the wavelength of the light source λ1=635 nm, the focaldistance f1=3.34, the numerical aperture NA1=0.60, infinityspecification.

[0653] When the wavelength of the light source λ2=780 nm, the focaldistance f2=3.36, the numerical aperture NA2=0.45, infinityspecification.

[0654] In this embodiment, in the light flux of λ1, an amount of +firstordered diffracted ray is generated to be greater than that of any otherordered diffracted ray. Also, in the light flux of λ2, an amount of+first ordered diffracted ray is generated to be greater than that ofany other ordered diffracted ray. Assuming that the diffractingefficiency of +first ordered diffracted ray for the light flux of λ1 is100%, the diffracting efficiency for the light flux of λ2 is 84%.Further, assuming that the diffracting efficiency of +first ordereddiffracted ray for the light flux of λ2 is 100%, the diffractingefficiency for the light flux of λ1 is 89%. TABLE 1 Surface No. R d₁ d₂n₁ n₂ νd nd 1 (Aspherical 2.126 2.2 2.2 1.53829 1.53388 56 1.5404surface 1 · diffraction surface) 2 (Aspherical −7.370 1.0 1.0 surface 2)3 Cover glass ∞ 0.6 1.2 1.58139 1.57346 30 1.585 4 ∞ (Subscript 1 is atλ₁ = 635 nm, subscript 2 is at λ₂ = 780 nm, νd and nd respectively showvalues to d-line.) Aspherical coefficient Aspherical surface 1Aspherical surface 2 κ = −0.10721 κ = −11.653 A4 = −0.0032315 A4 =0.0038456 A6 = −0.00058160 A6 = −0.020800 A8 = −4.6316 × 10⁻⁵ A8 =0.0078684 A10 = −3.79858 × 10⁻⁵ A10 = −0.0019431 A12 = −6.0308 × 10⁻⁶A12 = 0.00024343 Diffraction surface coefficient B2 = −96.766 B4 =−2.9950 B6 = 2.1306 B8 = −0.12614 B10 = −0.095285

Example 2, Example 3

[0655] Next, Example 2 and Example 3 will be described. Views of theoptical paths of the diffraction optical lens, which is the objectivelens in Example 2, to λ=405 nm and 635 nm will be respectively shown inFIG. 7 and FIG. 8. Further, in FIG. 9 and FIG. 10, views of thespherical aberration up to the numerical aperture 0.60 to λ=405 nm and635 nm for the diffraction optical lens in Example 2 will berespectively shown. Further, in FIG. 11 and FIG. 12, views of the wavefront aberration to the wavelengths λ=405 nm and 635 nm for thediffraction optical lens in Example 2 will be respectively shown.

[0656] Further, in FIG. 13 and FIG. 14, views of the optical paths ofthe diffraction optical lens, which is the objective lens in Example 3,to λ=405 nm and 635 nm will be respectively shown. Further, in FIG. 15and FIG. 16, views of the spherical aberration up to the numericalaperture 0.60 to λ=405 nm and 635 nm for the diffraction optical lens inExample 3 will be respectively shown. Further, in FIG. 17 and FIG. 18,views of the wave front aberration to the wavelengths λ=405 nm and 635nm for the diffraction optical lens in Example 3 will be respectivelyshown.

[0657] In Examples 2 and 3, the thickness of the substrates are both 0.6mm to the wavelength λ=405 nm and the wavelength λ=635 nm, and NA is0.6, and the wave front aberration is almost no aberration on theoptical axis, and even at the image height 0.03 mm, it is on the levelof practically almost no-aberration.

[0658] Lens data of Examples 2 and 3 will be shown below.

Example 2

[0659] When the wavelength of the light source λ1=405 nm, the focaldistance f1=3.23, the numerical aperture NA1=0.60, infinitespecification.

[0660] When the wavelength of the light source λ2=635 nm, the focaldistance f2=3.34, the numerical aperture NA2=0.60, infinitespecification.

[0661] In this embodiment, in the light flux of λ1, an amount of +firstordered diffracted ray is generated to be greater than that of any otherordered diffracted ray. Also, in the light flux of λ2, an amount of+first ordered diffracted ray is generated to be greater than that ofany other ordered diffracted ray. TABLE 2 Surface No. R d₁ d₂ n₁ n₂ νdnd 1 (Aspherical 2.128 2.2 2.2 1.55682 1.53829 56 1.5405 surface 1 ·diffraction surface) 2 (Aspherical −7.359 1.0 1.0 surface 2) 3 Coverglass ∞ 0.6 0.6 1.62230 1.58139 30 1.585 4 ∞ (Subscript 1 is at λ₁ = 405nm, subscript 2 is at λ₂ = 635 nm, νd and nd respectively show values tod-line.) Aspherical coefficient Aspherical surface 1 Aspherical surface2 κ = −0.15079 κ = −3.8288 A4 = −0.0021230 A4 = 0.0036962 A6 =−0.00076528 A6 = −0.020858 A8 = −8.84957 × 10⁻⁵ A8 = 0.0079732 A10 =−3.49803 × 10⁻⁵ A10 = −0.0018713 A12 = −2.38916 × 10⁻⁶ A12 = 0.00022504Diffraction surface coefficient B2 = 0.0 B4 = −6.7169 B6 = 2.0791 B8 =−0.31970 B10 = 0.00016708

Example 3

[0662] When the wavelength of the light source λ1=405 nm, the focaldistance f1=3.31, the numerical aperture NA1=0.60, infinitespecification.

[0663] When the wavelength of the light source λ2=635 nm, the focaldistance f2=3.34, the numerical aperture NA2=0.60, infinitespecification.

[0664] In this embodiment, in the light flux of λ1, an amount of +firstordered diffracted ray is generated to be greater than that of any otherordered diffracted ray. Also, in the light flux of λ2, an amount of+first ordered diffracted ray is generated to be greater than that ofany other ordered diffracted ray. TABLE 3 Surface No. R d₁ d₂ n₁ n₂ νdnd 1 (Aspherical 2.300 2.2 2.2 1.55682 1.53829 56 1.5404 diffractionsurface) 2 (Aspherical −7.359 1.0 1.0 surface 2) 3 Cover glass ∞ 0.6 0.61.62230 1.58139 30 1.585 4 ∞ (Subscript 1 is at λ₁ = 405 nm, subscript 2is at λ₂ = 635 nm, νd and nd respectively show values to d-line.)Aspherical coefficient Aspherical surface 1 Aspherical surface 2 κ =−0.19029 κ = 6.4430 A4 = 0.00030538 A4 = 0.037045 A6 = −0.0010619 A6 =−0.021474 A8 = −7.5747 × 10⁻⁵ A8 = 0.0078175 A10 = −6.7599 × 10⁻⁵ A10 =−0.0016064 A12 = −3.3788 × 10⁻⁶ A12 = 0.00014332 Diffraction surfacecoefficient B2 = −96.766 B4 = −2.9950 B6 = −0.25560 B8 = −0.08789 B10 =0.014562

Example 4, Example 5

[0665] Next, Example 4 and Example 5 on which the chromatic aberrationcorrection is conducted, will be described. Views of the optical pathsof the diffraction optical lens, which is the objective lens in Example4, will be respectively shown in FIG. 19. Further, in FIG. 20, views ofthe spherical aberration up to the numerical aperture 0.50 to λ=635 nm,650 nm and 780 nm for the diffraction optical lens in Example 4 will berespectively shown. Further, in FIG. 21, views of the optical paths ofthe diffraction optical lens, which is the objective lens in Example 5,will be respectively shown. Further, in FIG. 22, views of the sphericalaberration up to the numerical aperture 0.50 to λ=635 nm, 650 nm and 780nm for the diffraction optical lens in Example 5 will be respectivelyshown.

[0666] As can be seen from FIG. 20 and FIG. 22, according to thediffraction optical lens in Examples 4 and 5, to the wavelength λ=635 nmand the wavelength λ=780 nm, slippage due to color is almost perfectlycorrected, and to the wavelength λ=650 nm, it is also corrected to thedegree of practically no-problem.

[0667] Lens data of Examples 4 and 5 will be shown below.

Example 4

[0668] When the wavelength of the light source λ1=635 nm, the focaldistance f1=3.40, the numerical aperture NA1=0.50, infinitespecification.

[0669] When the wavelength of the light source λ2=780 nm, the focaldistance f2=3.41, the numerical aperture NA2=0.50, infinitespecification.

[0670] In this embodiment, in the light flux of λ1, an amount of +firstordered diffracted ray is generated to be greater than that of any otherordered diffracted ray. Also, in the light flux of λ2, an amount of+first ordered diffracted ray is generated to be greater than that ofany other ordered diffracted ray. TABLE 4 Surface No. R d₁ d₂ n₁ n₂ vdnd 1 (Aspherical 2.442 1.90 1.90 1.5417 1.5373 56 1.5438 surface 1 ·diffraction surface) 2 (Aspherical −5.990 1.68 1.68 surface 2) 3 Coverglass ∞ 1.20 1.20 1.5790 1.5708 30 1.5830 4 ∞ (Subscript 1 is at λ₁ =635 nm, subscript 2 is at λ₂ = 780 nm, vd and nd respectively showvalues to d-line.) Aspherical coefficient Aspherical surface 1Aspherical surface 2 k = −0.53245 k = 7.3988 A4 = 0.24033 × 10⁻² A4 =0.90408 × 10⁻² A6 = −0.91472 × 10⁻³ A6 = −0.18704 × 10⁻² A8 = 0.15590 ×10⁻⁴ A8 = −0.47368 × 10⁻³ A10 = −0.11131 × 10⁻³ A10 = 0.16891 × 10⁻³Diffraction surface coefficient b2 = −0.36764 × 10⁻² b4 = −0.91727 ×10⁻⁴ b6 = −0.34903 × 10⁻⁴ b8 = 0.77485 × 10⁻⁵ b10 = −0.15750 × 10⁻⁵

Example 5

[0671] When the wavelength of the light source λ1=635 nm, the focaldistance f1=3.40, the numerical aperture NA1=0.50, infinitespecification.

[0672] When the wavelength of the light source λ2=780 nm, the focaldistance f2=3.40, the numerical aperture NA2=0.50, infinitespecification.

[0673] In this embodiment, in the light flux of λ1, an amount of +firstordered diffracted ray is generated to be greater than that of any otherordered diffracted ray. Also, in the light flux of λ2, an amount of+first ordered diffracted ray is generated to be greater than that ofany other ordered diffracted ray. TABLE 5 Surface No. R d₁ d₂ n₁ n₂ vdnd 1 (Aspherical 2.160 1.80 1.80 1.5417 1.5373 56 1.5438 surface 1 ·diffraction surface) 2 (Aspherical −11.681 1.64 1.64 surface 2) 3 Coverglass ∞ 1.20 1.20 1.5790 1.5708 30 1.5830 4 ∞ (Subscript 1 is at λ₁ =635 nm, subscript 2 is at λ₂ = 780 nm, vd and nd respectively showvalues to d-line.) Aspherical coefficient Aspherical surface 1Aspherical surface 2 k = −0.17006 k = −40.782 A4 = −0.30563 × 10⁻² A4 =0.73447 × 10⁻² A6 = −0.45119 × 10⁻³ A6 = 0.85177 × 10⁻³ A8 = 0.58811 ×10⁻⁵ A8 = −0.82795 × 10⁻³ A10 = −0.13002 × 10⁻⁴ A10 = 0.23029 × 10⁻³Diffraction surface coefficient b2 = −0.74461 × 10⁻² b4 = 0.11193 × 10⁻²b6 = −0.85257 × 10⁻³ b8 = 0.50517 × 10⁻³ b10 = −0.11242 × 10⁻³

Examples 6-8

[0674] Next, Examples 6-8 will be described. Views of the optical pathsof the diffraction optical lenses, which are the objective lenses inExamples 6-8, to λ=650 nm will be respectively shown in FIG. 23, FIG. 30and FIG. 37. Further, in FIG. 24, FIG. 31 and FIG. 38, views of theoptical paths of the diffraction optical lenses in Example 6-8, to λ=780nm (NA=0.5) will be respectively shown. Further, in FIG. 25, FIG. 32 andFIG. 39, views of the spherical aberration up to the numerical aperture0.60 to λ=650±10 nm for the diffraction optical lenses in Examples 6-8will be respectively shown. Further, in FIG. 26, FIG. 33 and FIG. 40,views of the spherical aberration up to the numerical aperture 0.50 toλ=780±10 nm for the diffraction optical lenses in Examples 6-8 will berespectively shown. Further, in FIG. 27, FIG. 34 and FIG. 41, views ofthe spherical aberration up to the numerical aperture 0.60 to λ=780 nmfor the diffraction optical lenses in Examples 6-8 will be respectivelyshown.

[0675] Further, in FIG. 28, FIG. 35 and FIG. 42, views of the wave frontaberration rms to λ=650 nm for the diffraction optical lenses inExamples 6-8 will be respectively shown. Further, in FIG. 29, FIG. 36and FIG. 43, views of the wave front aberration rms to λ=780 nm for thediffraction optical lenses in Examples 6-8 will be respectively shown.Further, in FIG. 44, FIG. 45 and FIG. 46, graphs showing therelationship between the number of diffraction annular bands and theheight from the optical axis, for the diffraction optical lenses inExamples 6-8 will be respectively shown. Herein, the number ofdiffraction annular bands is defined as a value in which the phasedifference function is divided by 2π.

[0676] In Examples 6-8, as shown in the view of spherical aberration, atall apertures up to NA 0.60 to the wavelength λ=650 nm, there is almostno aberration. Further, to the wavelength λ=780 nm, up to NA 0.50 whichis a range of practical use, there is almost no aberration, however, inthe portion of NA 0.50-0.60 of the outside of it, the sphericalaberration is large, and it becomes the flare. According to this, to thewavelength λ=780 nm, an appropriate spot diameter can be obtained.

[0677] Next, lens data in Examples 6-8 will be shown. In [Table6]-[Table 8], STO expresses the diaphragm, and IMA expresses the imagesurface and is expressed in the form including the diaphragm.

Example 6

[0678] When the wavelength of the light source λ=650 nm, the focaldistance f=3.33, the image side numerical aperture NA=0.60, infinitespecification.

[0679] When the wavelength of the light source λ=780 nm, the focaldistance f=3.37, the image side numerical aperture NA=0.50 (NA=0.60),infinite specification. When a diameter of 13.5%-strength beam of 780 nmlight flux on the image forming surface is w, w=1.20 μm.

[0680] In this embodiment, as shown in FIG. 44, in the central sectionwhere a height from the optical axis is almost smaller than half of theeffective radius in the light flux of λ1 and the light flux of λ2, anamount of −first ordered diffracted ray is generated so as to be greaterthan that of any other ordered diffracted ray, and in the peripheralsection where a height from the optical axis is almost larger than halfof the effective radius, an amount of +first ordered diffracted ray isgenerated so as to be greater than that of any other ordered diffractedray. However, in the present embodiment, it may be possible that thesame ordered diffractive ray of the high order may be generated bymultiplying the pitch of annular bands with an integer instead of − or+first ordered diffracted ray.

[0681] Further, in the present embodiment, as shown in FIG. 27, in thesecond optical information recording medium, the spherical aberration atNA1=0.6 is +29 μm, and the spherical aberration at NA2=0.5 is +1 μm.

[0682] Further, in the present invention, the pitch of the diffractiveportion at NA=0.4 is 14 μm. TABLE 6 Surface No. R d n(λ = 650 nm) n(λ =780 nm) OBJ Infinity Infinity STO Infinity 0.0 2 (Aspheric   2.0575152.2 1.54113 1.53728 surface 1 Diffraction surface) 3 (Aspheric−7.8997731 1.0287 surface 2) 4 Infinity d4 1.57789 1.57079 5 Infinity d5IMA Infinity d4 d5 For λ = 650 nm 0.6 0.7500 For λ = 780 nm 1.2 0.35 Aspherical coefficient Aspherical surface 1 Aspherical surface 2 κ =−1.7952 κ = −3.452929 A4 = 0.51919725 × 10⁻² A4 = 0.15591292 × 10⁻¹ A6 =0.10988861 × 10⁻² A6 = −0.44528738 × 10⁻² A8 = −0.44386519 × 10⁻³ A8 =0.65423404 × 10⁻³ A10 = 5.4053137 × 10⁻⁵ A10 = −4.7679992 × 10⁻⁵Diffraction surface coefficient B2 = 29.443104 B4 = −14.403683 B6 =3.9425951 B8 = −2.1471955 B10 = 0.31859248

Example 7

[0683] When the wavelength of the light source λ=650 nm, the focaldistance f=3.33, the image side numerical aperture NA=0.60, infinitespecification.

[0684] When the wavelength of the light source λ=780 nm, the focaldistance f=3.37, the image side numerical aperture NA=0.50 (NA=0.60),infinite specification.

[0685] In this embodiment, as shown in FIG. 45, in the entire section,an amount of +first ordered diffracted ray is generated so as to begreater than that of any other ordered diffracted ray in the light fluxof λ1 and the light flux of λ2. However, in the present embodiment, itmay be possible that the same ordered diffractive ray of the high ordermay be generated by multiplying the pitch of annular bands with aninteger instead of +first ordered diffracted ray. TABLE 7 Surface No. Rd n(λ = 650 nm) n(λ = 780 nm) OBJ Infinity d0 STO Infinity 0.0 2(Aspheric   2.145844 2.2 1.54113 1.53728 surface 1 Diffraction surface)3 (Aspheric −7.706496 1.0326 surface 2) 4 Infinity d4 1.57789 1.57079 5Infinity d5 IMA Infinity d d4 d5 For λ = 650 nm Infinity 0.60 0.70 For λ= 780 nm 64.5 1.20 0.35 Aspherical coefficient Aspherical surface 1Aspherical surface 2 κ = −1.801329 κ = −8.871647 A4 = 0.1615422 × 10⁻¹A4 = 0.1492511 × 10⁻¹ A6 = −0.4937969 × 10⁻³ A6 = −0.4447445 × 10⁻² A8 =0.11038322 × 10⁻³ A8 = 0.60067143 × 10⁻³ A10 = −2.1823306 × 10⁻⁵ A10 =−3.4684206 × 10⁻⁵ Diffraction surface coefficient B2 = −17.150237 B4 =−4.1227045 B6 = 1.1902249 B8 = −0.26202222 B10 = 0.018845315

Example 8

[0686] For light source wavelength λ=650 nm

[0687] Focal distance f=3.33 Image side numerical aperture NA=0.60Infinity specification

[0688] For light source wavelength λ=780 nm

[0689] Focal distance f=3.35 Image side numerical aperture NA=0.50(NA=0.60) Infinity specification

[0690] w (Diameter of a beam of 13.5% intensity on an image formingplane of a light flux having a wavelength of 780 nm)=1.27 μm

[0691] In this embodiment, as shown in FIG. 46, in the light flux of λ1and the light flux of λ2, in only the extremely peripheral section, anamount of −first ordered diffracted ray is generated so as to be greaterthan that of any other ordered diffracted ray and in the other section,an amount of +first ordered diffracted ray is generated so as to begreater than that of any other ordered diffracted ray. However, in thepresent embodiment, it may be possible that the same ordered diffractiveray of the high order may be generated by multiplying the pitch ofannular bands with an integer instead of − or +first ordered diffractedray.

[0692] Further, in the present embodiment, as shown in FIG. 41, in thesecond optical information recording medium, the spherical aberration atNA1=0.6 is +68 μm, and the spherical aberration at NA2=0.5 is +9 μm.

[0693] Further, the pitch at NA=0.4 is 61 μm. TABLE 8 Surface No. R dn(λ = 650 nm) n(λ = 780 nm) OBJ Infinity d0 STO Infinity 0.0 2 (Aspheric  2.10598 2.2 1.54113 1.53728 surface 1 Diffraction surface) 3 (Aspheric−7.90392 1.0281 surface 2) 4 Infinity d4 1.57789 1.57079 5 Infinity d5IMA Infinity d4 d5 For λ = 650 nm 0.6 0.70 For λ = 780 nm 1.2 0.34Aspheric surface coefficient Aspheric surface 1 κ = −1.2532 A4 = 0.1007× 10⁻¹ A6 = −0.85849 × 10⁻³ A8 = −0.1.5773 × 10⁻⁵ A10 = 3.2855 × 10⁻⁵Aspheric surface 2 κ = −9.151362 A4 = 0.133327 × 10⁻¹ A6 = −0.378682 ×10⁻² A8 = 0.3001 × 10⁻³ A10 = 4.02221 × 10⁶ Diffraction surfacecoefficient B2 = 3.4251 × 10⁻²¹ B4 = 0.0763977 B6 = −5.5386 B8 = 0.05938B10 = 0.2224

[0694] Now, causes for fluctuation of a wavelength of a semiconductorlaser beam which enters a lens will be considered based on Examples 6-8.It is considered that individual dispersion of a wavelength of asemiconductor laser is ±2-±3 nm, a width of multi-mode oscillation isabout ±2 nm, and a mode hop for writing is about 2 nm. There will beexplained an occasion wherein fluctuation of spherical aberration of alens caused by wavelength fluctuation of a semiconductor laser which isalso caused by the causes stated above.

[0695] When a thickness of a transparent substrate of an optical disk isdifferent respectively for two light sources each having a differentwavelength, a lens corrected to be no-aberration for infinite light(parallel light flux) emitted from each of two light sources each havinga different wavelength has relatively large fluctuation of sphericalaberration, compared with wavelength fluctuation of about 10 nm for onelight source, as understood from data concerning Example 6. In Example6, though the wave-front aberration is 0.001 λrms in the wavelength of650 nm, it is deteriorated to about 0.035 λrms in the wavelength of 640nm and 660 nm. For an optical system with well-controlled laserwavelength, Example 6 can naturally be put to practical usesufficiently. On the contrary, in the case of a lens which is almostno-aberration for infinite light from either one light source and iscorrected to be almost no-aberration for finite light (non-parallellight flux) from the other wavelength light source, like the lens inExample 7, it is possible to control the spherical aberrationfluctuation to be extremely small, for wavelength fluctuation of about10 nm for one light source.

[0696] Next, temperature-caused capacity fluctuation of a diffractionoptical system (optical system having a diffraction optical lens) of thepresent embodiment will be explained. First, a wavelength of asemiconductor laser has a tendency to extend by 6 nm when temperaturerises by 30° C. On the contrary, when a diffraction optical system iscomposed of a plastic lens, the index of refraction has a tendency to bereduced by about 0.003-0.004 when temperature rises by 30° C. In thecase of a lens corrected to be no-aberration for infinite light for anyof two wavelengths like that in Example 6, a factor of a wavelength of asemiconductor laser caused by temperature change and a factor of theindex of refraction of a plastic lens caused by temperature changedisplay effect of mutual compensation, and make it possible to create anoptical system which is extremely resistant to temperature change.Further, in Example 6, even when raw material is glass, it is possibleto create an optical system having an allowable range for temperaturechange. Further, even in the case of Example 7, deterioration ofwave-front aberration is about 0.035 λrms for the temperature change of30° C. to be sufficient temperature compensation for practical use,which, however, is behind Example 6.

[0697] The compensation effect of temperature change stated above willfurther be explained. When recording and/or reproduction is conducted ontwo types of optical information recording media each having atransparent substrate with a different thickness by two light sourceseach having a different wavelength, it is possible to obtain imageforming characteristic which is the same as an exclusive objective lens,because it is possible to make the rms value of wave-front aberration tobe 0.07 of each wavelength or less even in the case of a numericalaperture required for information recording surface on each optical diskor in the case of a numerical aperture equal to or greater than theaforesaid aperture, by using an objective lens having a diffractionpattern. In ordered to make an optical pickup apparatus which isinexpensive and compact, a semiconductor laser is commonly used as alight source, and a plastic lens is commonly used as an objective lens.

[0698] There are various types of plastic materials which are used as alens, but their refractive index changes caused by temperature changeand their coefficient of linear expansion are greater than those ofglass. In particular, the refractive index changes caused by temperaturechange have an influence on various characteristics of a lens. In thecase of a plastic material used as an optical element of an opticalpickup, the refractive index change caused by temperature change in thevicinity of 25° C. is −0.0002/° C.-−0.00005/° C. Further, −0.0001/° C.is for the most of materials having low double refraction. Refractiveindex changes of thermosetting plastics used as a lens which are causedby temperature change are further greater, and some of them exceed theaforesaid range.

[0699] Even in the case of a semiconductor laser, an oscillationwavelength is dependent on temperature, as far as those manufactured bythe present technology are concerned, the oscillation wavelength changecaused by temperature change in the vicinity of 25° C. is 0.05 nm/°C.-0.5 nm/° C.

[0700] When a wave-front aberration of a light flux for reproducinginformation on an optical information recording medium or for recordinginformation on an optical information recording medium is changed bytemperature to cause an rms value to be 0.07 or more, it is difficult tomaintain the characteristics as an optical pickup apparatus. In the caseof the optical information medium of high density, in particular, it isnecessary to pay attention to the change of wave-front aberration causedby temperature. In the case of a wave-front aberration change of aplastic lens caused by temperature change, both of a shift of focus anda change of spherical aberration are caused by this wave-frontaberration change, but the latter is important because the focus controlis conducted in an optical pickup apparatus for the former. In thiscase, when the plastic material satisfies the relationship of

−0.0002/° C.<Δn/ΔT<−0.00005/° C.

[0701] when ΔT represents an amount of a change of a refractive indexfor the temperature change ΔT (° C.), and when a semiconductor lasersatisfies the relationship of

0.05 nm/° C.<Δλ1/ΔT<0.5 nm/° C.

[0702] when Δλ1 represents an amount of a change of oscillationwavelength for the temperature change ΔT, fluctuations of wave-frontaberration caused by refractive index change of a plastic lens caused bytemperature change and fluctuations of wave-front aberration caused by awavelength change of the semiconductor laser caused by temperaturechange act to contradict mutually, thereby, an effect of compensationcan be obtained.

[0703] When an amount of change of a component of cubic sphericalaberration of wave-front aberration for ambient temperature change of ΔT(° C.) is represented by ΔWSA3 (λrms), this is proportional to thefourth power of a numerical aperture (NA) of an objective lens on theoptical information medium side for a light flux passing through theobjective lens as well as to focal distance f (mm) of the plastic lens,and is inversely proportional to wavelength λ (mm) of the light sourcebecause the wave-front aberration is evaluated in a unit of wavelength.Therefore, the following expression holds,

ΔWSA3=k ·(NA)⁴ ·f·ΔT/λ  (a1)

[0704] wherein, k represents an amount which is dependent on a type ofan objective lens. Incidentally, a plastic double aspherical objectivelens optimized under the conditions that a focal distance is 3.36 mm, anumerical aperture on the optical information medium side is 0.6, and anincident light flux is a collimated light is described in MOC/GRIN '97Technical Digest C5 p40-p43, “The Temperature characteristics of a newoptical system with quasi-finite conjugate plastic objective for highdensity optical disk use” It is estimated that the wavelength λ is 650nm, because the graph in this document shows that WSA3 varies by 0.045λrms for the temperature change of 30° C., and thereby, the objectivelens is considered to be used for DVD. When the data stated above aresubstituted in expression (a1), K=2.2×10⁻⁶ is obtained. Though there isno description about an influence of wavelength change caused bytemperature change, when a change of oscillation wavelength is small, aninfluence of refractive index caused by temperature change is greater asfar as the objective lens using no diffraction is concerned.

[0705] With regard to the optical pickup apparatus for recording and/orreproducing concerning DVD, it is necessary that k is not more than theabove-mentioned value. When recording and/or reproducing for two typesof optical information recording media each having a transparentsubstrate with a different thickness, one can not ignore an influence ofwavelength change caused by temperature change, in an objective lenshaving a diffraction pattern. With regard to k, in particular, the valueof k varies depending on a focal distance, a refractive index change ofa plastic material caused by temperature change, a thickness differencebetween transparent substrates and a difference of oscillationwavelength between two light sources, and in Example 6, both a maincause of wavelength change of a semiconductor laser caused bytemperature change and a main cause of a refractive index change of aplastic lens caused by temperature change act to be effective forcompensation, and even when the objective lens is a plastic lens, achange of wave-front aberration caused by temperature change is small,resulting in λ=2.2×10⁻⁶/° C. and λ=0.4×10 ⁻⁶/° C. in simulation.

[0706] It is possible for k to take a range of 0.3<k<2.2. Therefore,from expression (a1), the following holds.

k=ΔWSA3·λ/{f·(NA1)⁴ ·ΔT(NA)}  (a2)

[0707] Therefore, the following holds.

0.3×10⁻⁶ /° C.<ΔWSA3·λ/{f·(NA1)⁴ ·ΔT}<2.2×10⁻⁶ /° C.  (a3)

[0708] In expression (a3), when the value of k exceeds the upper limit,it is difficult to maintain characteristics of an optical pickupapparatus due to temperature change, while when the lower limit isexceeded, it tends to be difficult to maintain characteristics of anoptical pickup apparatus in the case where a wavelength only is changed,though variation for temperature change is small.

[0709] In Example 8, by worsening efficiency of wavelength on one side,namely, of wavelength of 780 nm, slightly within an allowable range,compared with Example 6, it is possible to make the spherical aberrationvariation at ±10 nm in the vicinity of the wavelength on the other side,namely, of the wavelength of 650 nm to be small. Though wave-frontaberration at wavelength of 640 nm or 660 nm is about 0.035 λrms inExample 6, wave-front aberration at wavelength of 640 nm or 660 nm canbe improved to about 0.020 λrms in Example 8. These two factors are inthe relationship of trade-off, and it is important to have a balance,and when 0.07 λrms is exceeded, lens performance is deteriorated and itis difficult to use as an optical system for an optical disk.

[0710] Now, the relationship between diffraction power and a lens shapewill be explained. In FIG. 47, the relationship between diffractionpower and a lens shape is shown illustratively. FIG. 47(a) is a diagramshowing that diffraction power is a positive lens shape at all portions,while, FIG. 47(b) is a diagram showing that diffraction power is anegative lens shape at all portions. As shown in FIG. 47(c), a lens inFIG. 6 is designed so that diffraction power is negative in the vicinityof an optical axis and is changed to be positive on the half way. Due tothis, it is possible to prevent diffracting annular band whose pitch istoo fine. Further, by designing a lens so that diffraction power ischanged from the positive power to the negative one in the vicinity of aperipheral portion of the lens as shown in FIG. 8, it is also possibleto obtain satisfactory aberration between two wavelengths. It ispossible to arrange so that diffraction power is positive in thevicinity of an optical axis and is changed to the negative power on thehalf way, for example, as shown in FIG. 47(d).

[0711] In FIG. 47(c), a diffraction surface has plural diffractingannular bands which are blazed, and a step portion of the diffractingannular band which is closer to an optical axis is located to be awayfrom the optical axis, and a step portion of the diffracting annularband which is away from an optical axis is located to be closer to theoptical axis. In FIG. 47(d), a diffraction surface has pluraldiffracting annular bands which are blazed, and a step portion of thediffracting annular band which is closer to an optical axis is locatedto be closer to the optical axis, and a step portion of the diffractingannular band which is away from an optical axis is located to be awayfrom the optical axis.

Examples 9 and 10

[0712] An objective lens in Examples 9 and 10 has on its refractionsurface an aspherical shape shown by expression (a3), and Example 9 is afinite conjugate type complying with two light sources, and Example 10is a concrete example of an objective lens related to the secondembodiment and is a finite conjugate type complying with three lightsources. In Examples 9 and 10, the diffraction surface is expressed byexpression (a1) as phase difference function ΦB wherein a unit isradian.

[0713]FIGS. 50 and 51 show optical paths of the objective lens inExample 9 for λ=650 nm and λ=780 nm. FIG. 52 shows a diagram ofspherical aberration covering up to numerical aperture 0.60 of theobjective lens in Example 9 for λ=650 nm. FIGS. 53 and 54 show diagramsof spherical aberration covering up to numerical apertures 0.45 and 0.60of the objective lens in Example 9 for λ=780 nm. FIGS. 55 and 56 showdiagrams of wave-front aberration of the objective lens in Example 9 forwavelength λ=650 nm and λ=780 nm.

[0714] FIGS. 57-59 show optical paths of the objective lens in Example10 for λ=650 nm, λ=400 nm and λ=780 nm. FIGS. 61 and 61 show diagrams ofspherical aberration covering up to numerical apertures 0.65 of theobjective lens in Example 10 for λ=650 nm and λ=400 nm. FIGS. 62 and 63show diagrams of spherical aberration covering up to numerical apertures0.45 and 0.65 of the objective lens in Example 10 for λ=780 nm. FIGS.64-66 show wave-front aberration diagrams of the objective lens inExample 10 for λ=650 nm, λ=400 nm and λ=780 nm.

[0715] According to an objective lens in each of Examples 9 and 10, inany of the examples, a light flux exceeding NA 0.45 in practical usecauses large spherical aberration for light with wavelength of 780 nm,and it does not contribute to recording and/or reproduction ofinformation, as a flare.

[0716] Lens data of Examples 9 and 10 will be shown as follows. In Table9 and Table 10, r represents a radius of curvature of the lens, drepresents a distance between surfaces, n represents a refractive indexat each wavelength, and ν represents Abbe's number. As a reference,there will be described the refractive index for d line (λ=587.6 nm) andνd (Abbe's number). The figure for the surface number is shown includingan aperture, and in the present example, an air space is divided, forconvenience'sake, into two locations before and after the portioncorresponding to the transparent substrate of an optical disk.

Example 9

[0717] f=3.33 Image side NA 0.60 Magnification −0.194 (for wavelengthλ=650 nm)

[0718] f=3.35 Image side NA 0.45 (NA 0.60) Magnification −0.195 (forwavelength λ=780 nm) TABLE 9 nd vd Surface No. r d n n (Refer ence)Light source . 20.0 Aperture . 0.0 2 (Aspheric 2.2 1.53771 1.5388 1.540456.0 surface 1 · Diffraction surface) 2 (Aspheric 1.7467 1.58030 1.573461.585 29.9 surface 2) 4 . d4 5 . d5 Image point . d4 d5 for λ = 650 nm0.6 0.7500 for λ = 780 nm 1.2 0.3964 Aspheric surface 1  κ= −0.1295292A4 = −0.045445253 A8 = −0.00011777995 A10 = −5.3843777 × 10⁻⁵ A12 =−9.0807729 × 10⁻⁶ Diffraction surface 1 B2 = 0 B4 = −7.6489594 B6 =0.9933123 B8 = −0.28305522 B10 = 0.011289605 Aspheric surface 2 A4 =0.019003845 A6 = −0.010002187 A8 = 0.004087239 A10 = −0.00085994626 A12= 7.5491556 × 10⁻⁵

[0719] f = 3.31 Image side Magnification −0.203 (for NA 0.65 wavelengthλ = 650 nm) f = 3.14 Image side Magnification −0.190 (for NA 0.65wavelength λ = 400 nm) f = 3.34 Image side Magnification −0.205 (for NA0.65 wavelength λ = 780 nm)

[0720] TABLE 10 n n n (λ = (λ = (λ = Surface No. r d 650 nm) 400 nm) 780nm) Light source ∞ 20.0 Aperture ∞ 0.0 2 (Aspheric 2.450359 2.2 1.877071.92261 1.86890 surface 1 Diffraction surface 1) 3 (Aspheric 9.1083481.4503 surface 2 Diffraction surface 2) 4 ∞ d4 1.58030 1.62441 1.57346 5∞ d5 Image point ∞ for λ = 650 nm for λ = 400 nm for λ = 780 nm d4 0.60.6 1.2 d4 0.7500 0.5540 0.4097 Aspheric surface 1  κ = −0.08796008 A4 =−0.010351744 A6 = 0.0015514472 A8 = −0.00043894535 A10 = 5.481801 × 10⁻⁵A12 = −4.2588508 × 10⁻⁶ Diffraction surface 1  B2 = 0 B4 = −61.351934 B6= 5.9668445 B8 = −1.2923244 B10 = 0.041773541 Aspheric surface 2  κ =−302.6352 A4 = 0.002 A6 = −0.0014 A8 = 0.0042 A10 = −0.0022 A12 = 0.0004Diffraction surface 2  B2 = 0 B4 = 341.19136 B6 = −124.16233 B8 =49.877242 B10 = −5.9599182

[0721] Incidentally, the concrete example of the objective lens in theExample 10 can also be applied equally to the third embodiment.

Examples 11-14

[0722] An objective lens in each of Examples 11-14 has on its refractionsurface an aspherical shape shown by expression (a3). In Examples 11-13,the diffraction surface is expressed by expression (a1) as phasedifference function ΦB wherein a unit is radian. In Example 14, thediffraction surface is expressed by expression (a2) as optical pathdifference function Φb wherein a unit is mm.

[0723] When obtaining characteristics of an objective lens in each ofthe Examples 11-14, a light source wavelength for the first optical disk(DVD) is made to be 650 nm, a light source wavelength for the secondoptical disk (advanced high density optical disk employing blue laser)is made to be 400 nm, and transparent substrate thickness t1 for both ofthe first optical disk and the second optical disk is 0.6 mm. The lightsource wavelength for the third optical disk (CD) having transparentsubstrate thickness t2 which is different from t1 and is 1.2 mm was madeto be 780 nm. Numerical apertures NA corresponding respectively to lightsource wavelengths 400 nm, 650 nm and 780 nm are assumed to be 0.65,0.65 and 0.5.

Example 11

[0724] Example 11 is a concrete example of an objective lens related tothe fourth embodiment, and it is structured so that a collimated lightenters the objective lens. In this example, the square terms are notincluded in coefficients of the phase difference function, andcoefficients of terms other than the square terms only are used.

[0725] FIGS. 68-70 show diagrams for the optical path of the objectivelens in Example 11 respectively for λ=650 nm. λ=400 nm and λ=780 nm.FIG. 71 and FIG. 72 show the diagrams of spherical aberration of theobjective lens in Example 11 up to numerical aperture 0.65, respectivelyfor λ=650 nm and λ400 nm. FIG. 73 and FIG. 74 show the diagrams ofspherical aberration of the objective lens in Example 11 up to numericalaperture 0.45 and numerical aperture 0.65, for wavelength λ=780 nm.FIGS. 75-77 show diagrams of spherical aberration of the objective lensin Example 11 respectively for λ=650 nm, λ=400 nm and λ=780 nm.

[0726] Lens data of Example 11 will be shown as follows. In Table 11, rrepresents a radius of curvature of the lens, d represents a distancebetween surfaces and n represents a refractive index at each wavelength.The figure for the surface number is shown including an aperture.

Example 11

[0727] f = 3.33 Image side NA 0.65 (for wavelength λ = 650 nm) f = 3.15Image side NA 0.65 (for wavelength λ = 400 nm) f = 3.37 Image side NA0.45 (for wavelength λ = 780 nm) (NA 0.65)

[0728] TABLE 11 n n n (λ = (λ = (λ = Surface No. r d 650 nm) 400 nm) 780nm) Aperture ∞ 0.0 2 (Aspheric 2.177303 2.2 1.80256 1.84480 1.79498surface 1 Diffraction surface 1) 3 (Aspheric 6.457315 0.6985 surface 2Diffraction surface 2) 4 ∞ d4 1.58030 1.62441 1.57346 5 ∞ d5 Image point∞ for λ = 650 nm for λ = 400 nm for λ = 780 nm d4 0.6 0.6 1.2 d4 0.75000.6228 0.3995 Aspheric surface 1 κ = −0.1847301 A4 = −0.0090859227 A6 =0.0016821871 A8 = −0.0071180761 A10 = 0.00012406905 A12 = −1.4004589 ×10⁻⁵ Diffraction surface 1  B2 = 0 B4 = −69.824562 B6 = 0.35641549 B8 =0.6877372 B10 = −0.18333885 Aspheric surface 2  κ = −186.4056 A4 = 0.002A6 = −0.0014 A8 = 0.0042 A10 = −0.0022 A12 = 0.0004 Diffraction surface2  B2 = 0 B4 = 745.72117 B6 = −334.75078 B8 = 81.232224 B10 = −5.3410176

[0729] In an optical pickup apparatus having therein an objective lenslike that in Example 11 (and Example 12 which will be described later)and three light sources, it is possible to correct spherical aberrationcaused by the difference of transparent substrate thickness andchromatic aberration of spherical aberration caused by the difference ofwavelength for each disk, by designing aspherical surface coefficientsand coefficients of a phase difference function. As is clear from FIG.74, an outside of the numerical aperture NA 0.45 in practical use ismade to be flare on the third optical disk.

Example 12

[0730] An objective lens of Example 12 is structured so that divergedlight from a finite distance may enter the objective lens. In thisexample, the square terms are not included in coefficients of the phasedifference function, and coefficients of terms other than the squareterms only are used.

[0731] FIGS. 78-80 show diagrams for the optical path of the objectivelens in Example 12 respectively for λ=650 nm. λ=400 nm and λ=780 nm.FIG. 81 and FIG. 82 show the diagrams of spherical aberration of theobjective lens in Example 12 up to numerical aperture 0.65, respectivelyfor λ=650 nm and λ=400 nm. FIG. 83 and FIG. 84 show the diagrams ofspherical aberration of the objective lens in Example 12 up to numericalaperture 0.45 and numerical aperture 0.65, for wavelength λ=780 nm.FIGS. 85-87 show diagrams of spherical aberration of the objective lensin Example 12 respectively for λ=650 nm, λ=400 nm and λ=780 nm.

[0732] Lens data of Example 12 will be shown as follows.

Example 12

[0733] f = 3.31 Image side Magnification −0.203 (for NA 0.65 wavelengthλ = 650 nm) f = 3.14 Image side Magnification −0.190 for NA 0.65wavelength λ = 400 nm) f = 3.34 Image side Magnification −0.205 for NA0.65 wavelength (NA 0.65) λ = 780 nm)

[0734] TABLE 12 n n n (λ = (λ = (λ = Surface No. r d 650 nm) 400 nm) 780nm) Light source ∞ 20.0 Aperture ∞ 0.0 2 (Aspheric 2.450359 2.2 1.877071.92261 1.86890 surface 1 Diffraction surface 1) 3 (Aspheric 9.1083481.4503 surface 2 Diffraction surface 2) 4 ∞ d4 1.58030 1.62441 1.57346 5∞ d5 Image point ∞ for λ = 650 nm for λ = 400 nm for λ = 780 nm d4 0.60.6 1.2 d4 0.7500 0.5540 0.4097 Aspheric surface 1 κ = −0.08796008 A4 =−0.010351744 A6 = 0.0015514472 A8 = −0.00043894535 A10 = 5.481801 × 10⁻⁵A12 = −4.2588508 × 10⁻⁶ Diffraction surface 1  B2 = 0 B4 = −61.351934 B6= 5.9668445 B8 = −1.2923244 B10 = 0.041773541 Aspheric surface 2  κ =−302.6352 A4 = 0.002 A6 = −0.0014 A8 = 0.0042 A10 = −0.0022 A12 = 0.0004Diffraction surface 2  B2 = 0 B4 = 341.19136 B6 = −124.16233 B8 =49.877242 B10 = −5.9599182

[0735] In an optical pickup apparatus having therein an objective lenslike that in Example 12 and three light sources, it is possible tocorrect spherical aberration caused by the difference of transparentsubstrate thickness and chromatic aberration of spherical aberrationcaused by the difference of wavelength, for each disk. As is clear fromFIG. 84, an outside of the numerical aperture NA 0.45 in practical useis made to be flare on the third optical disk.

Example 13

[0736] An objective lens of Example 13 is another concrete example of anobjective lens related to the fourth embodiment, and is structured sothat collimated light from an infinite distance may enter the objectivelens. In this example, the square terms and terms other than the squareterm are used as coefficients of the phase difference function of thediffraction surface.

[0737] FIGS. 88-90 show diagrams for the optical path of the objectivelens in Example 13 respectively for λ=650 nm. λ=400 nm and λ=780 nm.FIG. 91 and FIG. 92 show the diagrams of spherical aberration of theobjective lens in Example 13 up to numerical aperture 0.60, respectivelyfor λ=650 nm and λ=400 nm. FIG. 93 and FIG. 94 show the diagrams ofspherical aberration of the objective lens in Example 13 up to numericalaperture 0.45 and numerical aperture 0.60, for wavelength λ=780 nm.FIGS. 95-97 show diagrams of spherical aberration of the objective lensin Example 13 respectively for λ=650 nm, λ=400 nm and λ=780 nm.

[0738] Lens data of Example 13 will be shown as follows.

Example 13

[0739] f = 3.31 Image side NA 0.60 (for wavelength λ = 650 nm) f = 3.14Image side NA 0.60 (for wavelength λ = 400 nm) f = 3.34 Image side NA0.45 (for wavelength λ = 780 nm) (NA 0.60)

[0740] TABLE 13 n n n (λ = (λ = (λ = Surface No. r d 650 nm) 400 nm) 780nm) Aperture ∞ 0.0 2 (Aspheric 2.016831 2.2 1.53771 1.55765 1.53388surface 1 Diffraction surface 1) 3 (Aspheric −12.04304 0.7555 surface 2Diffraction surface 2) 4 ∞ d4 1.58030 1.62441 1.57346 5 ∞ d5 Image point∞ for λ = 650 nm for λ = 400 nm for λ = 780 nm d4 0.6 0.6 1.2 d4 0.75000.7500 0.3409 Aspheric surface 1 κ = −0.3363369 A4 = −0.0025421455 A6 =−0.0010660122 A8 = 4.7189743 × 10⁻⁵ A10 = 1.5406396 × 10⁻⁶ A12 =−7.0004876 × 10⁻⁶ Diffraction surface 1 B2 = −177.66083 B4 = −46.296284B6 = −6.8014831 B8 = 1.6606499 B10 = −0.39075825 Aspheric surface 2  κ =43.44262 A4 = 0.002 A6 = −0.0014 A8 = 0.0042 A10 = −0.0022 A12 = 0.0004Diffraction surface 2  B2 = 241.52445 B4 = 402.41974 B6 = −191.87213 B8= 64.779696 B10 = −8.6741764

[0741] In the present example, it is possible to correct sphericalaberration caused by the difference of thickness of the transparentsubstrate and to correct chromatic aberration of spherical aberrationand axial chromatic aberration both caused by the difference ofwavelength, for each disk, because square terms and terms other than thesquare terms are used as coefficients of the phase difference functionof the diffraction surface. As is clear from FIG. 94, an outside of thenumerical aperture NA 0.45 in practical use is made to be flare on thethird optical disk.

Example 14

[0742] An objective lens of Example 14 is a concrete example of anobjective lens related to the sixth embodiment, and is structured sothat collimated light with wavelengths of 400 nm and 650 nm from aninfinite distance and diverged light with wavelength of 780 nm may enterthe objective lens. In this example, square terms and terms other thanthe square terms are used as coefficients of the phase differencefunction of the diffraction surface.

[0743]FIG. 98 shows a diagram for the optical path of the objective lensin Example 14 for λ=400 nm. FIGS. 99-101 show the diagrams of sphericalaberration of the objective lens in Example 14 up to numerical aperture0.65, respectively for λ=400 nm±10 nm, λ=650 nm±10 nm and λ=780 nm±10nm.

[0744] Lens data of Example 14 will be shown as follows.

Example 14

[0745] f = Image side NA 0.65 (for wavelength λ = 650 nm) f = Image sideNA 0.65 (for wavelength λ = 400 nm) f = Image side NA 0.45 (forwavelength λ = 780 nm) (NA 0.65)

[0746] TABLE 14 n n n (λ = Surface No. r d (λ = 650 nm) (λ = 400 nm) 780nm) Light source ∞ d0 Aperture ∞ 0 2 (Aspheric 2.15759 2.400 1.561 1.5411.537 surface 1 Diffraction surface) 3 (Aspheric 0.976 surface 2) 4 ∞ d41.622 1.578 1.571 5 ∞ d5 Image point ∞ for λ = 400 nm for λ = 650 nm forλ = 780 nm d0 ∞ ∞ 75.17 d4 0.6 0.6 1.2 d5 0.649 0.733 0.532 Focaldistance 3.33 3.44 3.46 Aspheric surface 1 κ = −2.0080 A4 = 0.18168 ×10⁻¹ A6 = −0.91791 × 10⁻³ A8 = 0.16455 × 10⁻³ A10 = −0.11115 × 10⁻⁴Diffraction surface b2 = −0.51589 × 10⁻³ b4 = −0.24502 × 10⁻³ b6 =0.49557 × 10⁻⁴ b8 = −0.14497 × 10⁻⁴ Aspheric surface 2 κ = 3.1831 A4 =0.14442 × 10⁻¹ A6 = −0.17506 × 10⁻² A8 = 0.21593 × 10⁻⁴ A10 = 0.12534 ×10⁻⁴

[0747] Incidentally, the invention is not limited to the examplesexplained above. Though the diffraction surface is formed on each ofboth sides of the objective lens, it may also be provided on a certainsurface of an optical element in an optical system of the optical pickupapparatus. Further, though the ring-zonal diffraction surface is formedon the entire surface of the lens, it may also be formed partially. Inaddition, though optical design has been advanced under the assumptionthat a light source wavelength is 400 nm and a thickness of atransparent substrate is 0.6 mm, for the target of an advanced highdensity optical disk employing blue laser, the invention can also beapplied to the optical disk with specifications other than the aforesaidspecifications.

[0748] Next, the seventh embodiment of the invention will be explainedas follows.

[0749]FIG. 117 shows a schematic structure of an objective lens and anoptical pickup apparatus including the objective lens in the presentembodiment. As is shown in FIG. 117, first semiconductor laser 111 andsecond semiconductor laser 112 are unitized as a light source. Betweencollimator 13 and objective lens 16, there is arranged beam splitter 120through which a beam collimated mostly by the collimator 13 passes toadvance to the objective lens 16. Further, the beam splitter 120 servingas an optical path changing means changes an optical path of a lightflux reflected on information recording surface 22 so that the lightflux may advance to optical detector 30. The objective lens 16 has onits peripheral portion flange section 16 a which makes it easy to mountthe objective lens 16 on the optical pickup apparatus. Further, sincethe flange section 16 a has its surface extending in the direction whichis almost perpendicular to an optical axis of the objective lens 16, itis possible to mount the objective lens more accurately.

[0750] When reproducing the first optical disk, a light flux emittedfrom the first semiconductor laser 111 passes through collimator 13 tobecome a collimated light flux which further passes through beamsplitter 120 to be stopped down by aperture 17, and is converged byobjective lens 16 on information recording surface 22 throughtransparent substrate 21 of the first optical disk 20. Then, the lightflux modulated by information bits and reflected on the informationrecording surface 22 is reflected on beam splitter 120 through aperture17, then, is given astigmatism by cylindrical lens 180, and entersoptical detector 30 through concave lens 50. Thereby, signals outputtedfrom the optical detector 30 are used to obtain reading signals ofinformation recorded on the first optical disk 20.

[0751] Further, a change in quantity of light caused by a change inshape and position of a spot on the optical detector 30 is detected todetect a focused point and a track. Based on this detection, objectivelens 16 is moved so that a light flux from the first semiconductor laser111 may be caused by two-dimensional actuator 150 to form an image oninformation recording surface 22 on the first optical disk 20, andobjective lens 16 is moved so that a light flux from the firstsemiconductor laser 111 may form an image on a prescribed track.

[0752] When reproducing the second optical disk, a light flux emittedfrom the second semiconductor laser 112 passes through collimator 13 tobecome a collimated light flux which further passes through beamsplitter 120 to be stopped down by aperture 17, and is converged byobjective lens 16 on information recording surface 22 throughtransparent substrate 21 of the second optical disk 20. Then, the lightflux modulated by information bits and reflected on the informationrecording surface 22 is reflected on beam splitter 120 through aperture17, then, is given astigmatism by cylindrical lens 180, and entersoptical detector 30 through concave lens 50. Thereby, signals outputtedfrom the optical detector 30 are used to obtain reading signals ofinformation recorded on the second optical disk 20. Further, a change inquantity of light caused by a change in shape and position of a spot onthe optical detector 30 is detected to detect a focused point and atrack. Based on this detection, objective lens 16 is moved so that alight flux from the first semiconductor laser 112 may be caused bytwo-dimensional actuator 15 to form an image on information recordingsurface 22 on the second optical disk 20, and objective lens 16 is movedso that a light flux from the second semiconductor laser 112 may form animage on a prescribed track.

[0753] Objective lens (diffraction lens) 16 is designed so that itswave-front aberration may be 0.07 λrms or less for each wavelength (λ)for incident light from each semiconductor laser, up to the numericalaperture (maximum numerical aperture which is greater than thosenecessary-for recording and/or reproducing of the first and secondoptical disks. Therefore, the wave-front aberration on the image formingsurface of each light flux is 0.07 λrms or less. Accordingly, no flareis caused on an image forming surface and on the detector 30 whenrecording and/or reproducing either disk, resulting in bettercharacteristics for focusing error detection and track error detection.

[0754] Incidentally, there are assumed a case wherein the first opticaldisk is DVD (light source wavelength 650 nm) and the second optical diskis CD (light source wavelength 780 nm), and a case wherein the firstoptical disk is an advanced high density disk (light source wavelength400 nm) and the second optical disk is DVD (light source wavelength 650nm). In particular, when there is a big difference between necessarynumerical apertures of both optical disks like the aforesaid occasion, aspot is sometimes too small compared with a necessary spot diameter. Inthis case, an aperture regulating means explained in other places inthis document can be introduced to obtain the desired spot diameter.

[0755] Examples 15, 16, 17 and 18 for spherical-aberration-correctedlens will be explained as follows, as a concrete example of an objectivelens related to the seventh embodiment. In each example, the wave-frontaberration is corrected to be 0.07 λrms or less for the maximumnumerical aperture. Incidentally, the image side mentioned in thefollowing explanation means the optical information recording mediumside.

Example 15

[0756]FIG. 118 shows a diagram of an optical path of a diffractionoptical lens (objective lens having a diffraction surface) representingthe objective lens in Example 15. FIG. 119 shows a spherical aberrationdiagram up to numerical aperture 0.60 for wavelengths (λ)=640, 650 and660 nm concerning the diffraction optical lens of Example 15. FIG. 120shows a diagram of an optical path of the diffraction optical lens ofthe Example 15 wherein the thickness of the transparent substrate of theoptical information recording medium is greater than that in FIG. 118.FIG. 121 shows diagrams of spherical aberration up to numerical aperture0.60 for wavelengths λ=770, 780 and 790 nm concerning the diffractionoptical lens in the case of FIG. 120.

[0757] According to the diffraction optical lens of Example 15, allapertures up to NA 0.60 are almost no-aberration for wavelength λ=650 nmas shown in FIG. 119. As shown in FIGS. 120 and 121 where thetransparent substrate is thick, all apertures up to NA 0.60 are almostno-aberration for wavelength λ=780 nm. Incidentally, a prescribednumerical aperture for λ=780 nm is 0.45.

[0758] As stated above, in the Example 15, the spherical aberration inthe case of wavelength 780 nm where the transparent substrate of theoptical information recording medium is thicker than that in Examples 1,6 and 8 can be corrected up to the numerical aperture (NA 0.60) which isthe same as that in the case where the transparent substrate is thinnerand wavelength is 650 nm.

[0759] Lens data in Example 15 will be shown as follows.

[0760] For wavelength λ=650 nm,

[0761] Focal distance f=3.33 Numerical aperture on the image sideNA=0.60 Infinite specification (incident collimated light flux)

[0762] (0453

[0763] For wavelength λ=780 nm,

[0764] Focal distance f=3.38 Numerical aperture on the image sideNA=0.60 Infinite specification TABLE 15 Surface No. R d n(λ = 650 nm)n(λ = 780 nm) OBJ Infinity Infinity STO Infinity 0.0 2 (Aspheric  2.06085 2.2 1.54113 1.53728 surface 1 Diffraction surface) 3 (Aspheric−6.98986 1.059 surface 2) 4 Infinity d4 1.57787 1.57084 5 Infinity d5 d4d5 For λ = 650 nm 0.6 0.700 For λ = 780 nm 1.2 0.364 Aspheric surfacecoefficient Aspheric surface 1 K = −1.0358 A₄ = 4.8632 × 10⁻³ A₆ =5.3832 × 10⁻⁴ A₆ = −1.5773 × 10⁻⁴ A₁₀ = 3.8683 × 10⁻⁷ Aspheric surface 2K = −9.256352 A₄ = 1.5887 × 10⁻² A₆ = −5.97422 × 10⁻³ A₆ = 1.11613 ×10⁻³ A₁₀ = −9.39682 × 10⁻⁵ Diffraction surface coefficient(Standardwavelength 650 nm) b₂ = 6.000 × 10⁻³ b₄ = −1.317 × 10⁻³ b₆ = 1.5274 ×10⁻⁴ b₈ = −6.5757 × 10⁻⁵ b₁₀ = 6.2211 × 10⁻⁶

Example 16

[0765]FIG. 122 shows a diagram of an optical path of a diffractionoptical lens (objective lens having a diffraction surface) representingthe objective lens in Example 16. FIG. 123 shows a spherical aberrationdiagram up to numerical aperture 0.60 for wavelengths (λ)=640, 650 and660 nm concerning the diffraction optical lens of Example 16. FIG. 124shows a diagram of an optical path of the diffraction optical lens ofthe Example 16 wherein the thickness of the transparent substrate of theoptical information recording medium is greater than that in FIG. 122.FIG. 125 shows diagrams of spherical aberration up to numerical aperture0.60 for wavelengths λ=770, 780 and 790 nm concerning the diffractionoptical lens in the case of FIG. 124.

[0766] According to the diffraction optical lens of Example 16, allapertures up to NA 0.60 are almost no-aberration for wavelength λ=650 nmas shown in FIG. 123. As shown in FIGS. 124 and 125 where thetransparent substrate is thick, all apertures up to NA 0.60 are almostno-aberration for wavelength λ=780 nm. Incidentally, a prescribednumerical aperture for λ=780 nm is 0.45.

[0767] As stated above, in the Example 16, the spherical aberration inthe case of wavelength 780 nm where the transparent substrate of theoptical information recording medium is thicker than that in Examples 1,6 and 8 can be corrected up to the numerical aperture (NA 0.60) which isthe same as that in the case where the transparent substrate is thinnerand wavelength is 650 nm. Incidentally, in Examples 15 and 16, apowerful correcting action for spherical aberration caused bydiffraction is necessary for correcting spherical aberration caused by adifference in transparent substrate thickness up to NA 0.6. For thisreason, a ring-zonal pitch is reduced, but the reduction of the pitch isrelieved by making the paraxial power of diffraction to be negative.

[0768] Lens data in Example 16 will be shown as follows.

[0769] For wavelength λ=650 nm,

[0770] Focal distance f=3.33 Numerical aperture on the image sideNA=0.60 Infinite specification

[0771] (0463

[0772] For wavelength λ=780 nm,

[0773] Focal distance f=3.36 Numerical aperture on the image sideNA=0.60 Infinite specification TABLE 16 Surface No. R d n(λ = 650 nm)n(λ = 780 nm) OBJ Infinity Infinity STO Infinity 0.0 2 (Aspheric  2.09216 2.200 1.54113 1.53728 surface 1 Diffraction surface) 3(Aspheric −7.49521 1.024 surface 2) 4 Infinity d4 1.57787 1.57084 5Infinity d5 d4 d5 For λ = 650 nm 0.6 0.699 For λ = 780 nm 1.2 0.345Aspheric surface coefficient Aspheric surface 1 K = −1.1331 A₄ = 4.5375× 10⁻³ A₆ = 1.2964 × 10⁻³ A₆ = −3.6164 × 10⁻⁴ A₁₀ = 2.0765 × 10⁻⁵Aspheric surface 2 K = −4.356298 A₄ = 1.57427 × 10⁻² A₆ = −4.91198 ×10⁻³ A₆ = 7.72605 × 10⁻⁴ A₁₀ = −5.75456 × 10⁻⁵ Diffraction surfacecoefficient(Standard wavelength 650 nm) b₂ = 2.1665 × 10⁻³ b₄ = −2.0272× 10⁻³ b₆ = 5.5178 × 10⁻⁴ b₈ = −1.8391 × 10⁻⁴ b₁₀ = 1.8148 × 10⁻⁵

Example 17

[0774]FIG. 126 shows a diagram of an optical path of a diffractionoptical lens (objective lens having a diffraction surface) representingthe objective lens in Example 17. FIG. 127 shows a spherical aberrationdiagram up to numerical aperture 0.60 for wavelengths (λ)=640, 650 and660 nm concerning the diffraction optical lens of Example 17. FIG. 128shows a diagram of an optical path of the diffraction optical lens ofthe Example 17 wherein the thickness of the transparent substrate of theoptical information recording medium is greater than that in FIG. 126.FIG. 129 shows diagrams of spherical aberration up to numerical aperture0.60 for wavelengths λ=770, 780 and 790 nm concerning the diffractionoptical lens in the case of FIG. 128.

[0775] According to the diffraction optical lens of Example 17, allapertures up to NA 0.60 are almost no-aberration for wavelength λ=650 nmas shown in FIG. 127. As shown in FIGS. 128 and 129 where thetransparent substrate is thick, all apertures up to NA 0.60 are almostno-aberration for wavelength λ=780 nm. Incidentally, a prescribednumerical aperture for λ=780 nm is 0.45. Axial chromatic aberration ineach of Examples 15-17 is different from others, and a ring-zonal pitchis also different from others.

[0776] As stated above, in the Example 17, the spherical aberration inthe case of wavelength 780 nm where the transparent substrate of theoptical information recording medium is thicker than that in Examples 1,6 and 8 can be corrected up to the numerical aperture (NA 0.60) which isthe same as that in the case where the transparent substrate is thinnerand wavelength is 650 nm.

[0777] Lens data in Example 17 will be shown as follows.

[0778] For wavelength λ=650 nm,

[0779] Focal distance f=3.33 Numerical aperture on the image sideNA=0.60 Infinite specification

[0780] For wavelength λ=780 nm,

[0781] Focal distance f=3.34 Numerical aperture on the image sideNA=0.60 Infinite specification TABLE 17 Surface No. R d n (λ = 650 nm) n(λ = 650 nm) OBJ Infinity Infinity STO Infinity 2 (Aspheric  2.147572.200 1.54113 1.53728 surface 1 Diffraction surface) 3 (Aspheric−7.74682 1.0333 surface 2) 4 Infinity d4 1.57787 1.57084 5 Infinity d5d4 d5 For λ = 650 nm 0.6 0.700 For λ = 780 nm 1.2 0.327 Aspheric surfacecoefficient Aspheric surface 1 K = −1.0751 A₄ = 5.0732 × 10⁻³ A₆ =4.3722 × 10⁻⁴ A₈ = −1.4774 × 10⁻⁴ A₁₀ = 9.6694 × 10⁻⁷ Aspheric surface 2K = −10.41411 A₄ = 1.59463 × 10⁻² A₆ = −6.02963 × 10⁻³ A₈ = 1.11268 ×10⁻³ A₁₀ = −9.3151 × 10⁻⁵ Diffraction surface coefficient (Standardwavelength 650 nm) b₂ = −2.000 × 10⁻³ b₄ = −1.4462 × 10⁻³ b₆ = 1.1331 ×10⁻⁴ b₈ = −6.6211 × 10⁻⁵ b₁₀ = 6.8220 × 10⁻⁶

Example 18

[0782]FIG. 130 shows a diagram of an optical path of a diffractionoptical lens (objective lens having a diffraction surface) representingthe objective lens in Example 18. FIG. 131 shows a spherical aberrationdiagram up to numerical aperture 0.70 for wavelengths (λ)=390, 400 and410 nm concerning the diffraction optical lens of Example 18. FIG. 132shows a diagram of an optical path of the diffraction optical lens ofthe Example 18 wherein the thickness of the transparent substrate of theoptical information recording medium is greater than that in FIG. 130.FIG. 133 shows diagrams of spherical aberration up to numerical aperture0.70 for wavelengths λ=640, 650 and 660 nm concerning the diffractionoptical lens in the case of FIG. 132.

[0783] According to the diffraction optical lens of Example 18, allapertures up to NA 0.70 are almost no-aberration for wavelength λ=400 nmas shown in FIG. 131. As shown in FIGS. 132 and 133 where thetransparent substrate is thick, all apertures up to NA 0.70 are almostno-aberration for wavelength λ=650 nm.

[0784] As stated above, in the Example 17, the spherical aberration inthe case of wavelength 650 nm where the transparent substrate of theoptical information recording medium is thicker than that in Examples 1,6 and 8 can be corrected up to the numerical aperture (NA 0.70) which isthe same as that in the case where the transparent substrate is thinnerand wavelength is 400 nm.

[0785] Lens data in Example 18 will be shown as follows.

[0786] For wavelength λ=400 nm,

[0787] Focal distance f=3.33 Numerical aperture on the image sideNA=0.70 Infinite specification

[0788] For wavelength λ=650 nm,

[0789] Focal distance f=3.43 Numerical aperture on the image sideNA=0.70 Infinite specification TABLE 18 Surface No. R d n (λ = 650 nm) n(λ = 650 nm) OBJ Infinity Infinity STO Infinity 2 (Aspheric  2.658582.40  1.71657 1.68987 surface 1 Diffraction surface) 3 (Aspheric−15.86969 1.297 surface 2) 4 Infinity d4 1.62158 1.57787 5 Infinity d5d4 d5 For λ = 650 nm 0.1 0.704 For λ = 780 nm 0.6 0.469 Aspheric surfacecoefficient Aspheric surface 1 K = 0.0 A₄ = −7.9616 × 10⁻⁴ A₆ = −5.7265× 10⁻⁴ A₈ = 8.3209 × 10⁻⁵ A₁₀ = −4.1599 × 10⁵ Aspheric surface 2 K = 0.0A₄ = 3.11131 × 10⁻² A₆ = −1.18548 × 10⁻² A₈ = 1.63937 × 10⁻³ A₁₀ =−6.60514 × 10⁻⁴ Diffraction surface coefficient (Standard wavelength 400nm) b₂ = −1.4046 × 10⁻³ b₄ = −8.6959 × 10⁻⁴ b₆ = 2.3488 × 10⁻⁴ b₈ =−5.2455 × 10⁻⁵ b₁₀ = 3.6385 × 10⁻⁶

[0790] Next, a pitch of plural annular bands of a diffraction opticallens in each of the Examples 1-3 and Examples 14-18 will be explained.Each of the plural annular bands is formed to be almost in a form of aconcentric circle whose center is an optical axis, and values of pitchPf (mm) of the annular band corresponding to the maximum numericalaperture of the lens on the image side, pitch Pf (mm) of the annularband corresponding to the numerical aperture representing a half of themaximum numerical aperture, and ((Ph/Pf) −2) are shown in Table 19.TABLE 19 Example Pf Ph Ph/Pf-2  1 0.009 0.110 10.2  2 0.067 0.255 1.8  30.012 0.032 0.67 14 0.039 0.221 3.7 15 0.027 0.091 1.4 16 0.014 0.35323.2 17 0.010 0.065 4.5 18 0.011 0.060 3.5

[0791] According to the further study of the inventors of the presentinvention, it has been found that when the aforesaid expression (b1)holds, namely, when the value of |(Ph/Pf)−2| is not less than the lowerlimit of the expression, the diffraction action to correct sphericalaberration of a high ordered is not attenuated, and therefore, adifference of spherical aberration between two wavelengths caused by adifference of thickness of transparent substrates can be corrected bythe diffraction action, while, when the aforesaid value is not more thanthe upper limit, a portion where the pitch of diffraction annular bandsis too small is hardly caused, and it is possible to manufacture a lenshaving high diffraction efficiency.

[0792] With regard to the aforesaid relational expression, the followingexpression (b2) is preferable, and expression (b3) is more preferable.

0.8≦|(Ph/Pf)−2|≦6.0  (b2)

1.2≦|(Ph/Pf)−2|≦2.0  (b3)

[0793] Next, 8th Embodiment of the invention will be explained.

[0794] Necessary numerical aperture NA1 of the objective lens on theoptical information recording medium side which is needed for recordingand reproducing DVD by the use of a light source having wavelength of650 nm is about 0.6, and necessary numerical aperture NA2 of theobjective lens on the optical information recording medium side which isneeded for reproducing CD by the use of a light source having wavelengthof 780 nm is about 0.45 (0.5 for recording). Therefore, the diffractionpattern for the correction of aberration stated above is notindispensable, up to numerical aperture NA1.

[0795] Further, the diffraction pattern is not indispensable in thevicinity of an optical axis, because a depth of focus is great and anamount of spherical aberration is small.

[0796] By forming a diffraction pattern on a necessary and least portionand by making the residual portion to be a refraction surface, it ispossible to prevent damage of a tool in the course of metal moldprocessing, to improve releasing property, and to prevent deteriorationof capacity which is caused when there is a thickness difference indisks caused by that a light-converging spot is narrowed down more thannecessary on the CD side, or is caused when a disk is inclined.

[0797] For this purpose, the diffraction pattern of the objective lensneeds to be rotation-symmetrical about an optical axis, and thefollowing conditions need to be satisfied, when +primary diffracted raycoming from the circumference of a circle of the diffraction pattern onthe objective lens farthest from the optical axis for the light fluxemitted from the first light source is converted into a light flux withnumerical aperture NAH1 on the optical information recording mediumside, and when +primary diffracted ray coming from the circumference ofa circle of the diffraction pattern on the objective lens closest to theoptical axis for the light flux emitted from the first light source isconverted into a light flux with numerical aperture NAL1 on the opticalinformation recording medium side.

NAH1<NA1

0≦NAL1≦NA2

[0798] When the first optical information recording medium is DVD,wavelength λ1 of the first light source is 650 nm, the second opticalinformation recording medium is CD and wavelength λ2 of the second lightsource is 780 nm, it is preferable that NAH1 is from 0.43 to 0.55 andNAL1 is from 0.10 to 0.40.

[0799] An optical design of an objective lens concerning the portionhaving a diffraction pattern is conducted so that +primary diffractedray of a light flux entering the objective lens from the first lightsource may be a light-converging spot which is almost no-aberration. Onthe other hand, an optical design of an objective lens concerning theportion having no diffraction pattern is conducted so that a light fluxentering the objective lens from the first light source may be alight-converging spot which is almost no-aberration.

[0800] Light-converging positions for both of them stated above need toagree mostly. Further, it is important that a phase of each light fluxagrees with others. Incidentally, with regard to the phase, when krepresents a small integer, light-converging characteristic under thedesigned wavelength is hardly changed despite deviation of 2kπ, but whenan absolute value of |k| is great, the light-converging characteristicis easily changed by the wavelength fluctuation. It is preferable that|k| is in a range of 1-10.

[0801] Among light fluxes emitted from the second light source, in thiscase, +primary diffracted ray from the circumference of a circle ofdiffraction pattern on the objective lens which is farthest from anoptical axis is converted into a light flux whose numerical aperture onthe optical information recording medium side is NAH2, and concurrentlywith this, +primary diffracted ray from the circumference of a circle ofthe diffraction pattern which is closest to an optical axis is convertedinto a light flux whose numerical aperture on the optical informationrecording medium side is NAL2.

[0802] Spherical aberration of a light flux passing through an objectivelens is established, so that a light-converging position and a phasedifference for each of a light flux from a portion having a diffractionpattern and a light flux from a portion having no diffraction patternmay be optimum, and thereby, a spot making recording and reproduction ofthe second optical information recording medium possible may be formedon an information recording surface of the optical information recordingmedium by the use of a light flux whose numerical aperture through anobjective lens is NAH2 or less, among light fluxes emitted from thesecond light source.

[0803] In practice, it is preferable that wave-front aberration at abest image point through a transparent substrate of the first opticalinformation recording medium for a light flux whose numerical aperturethrough an objective lens is NA1 or less among light fluxes emitted fromthe first light source is 0.07 λrms or less, and wave-front aberrationat a best image point through a transparent substrate of the secondoptical information recording medium for a light flux whose numericalaperture through an objective lens is NAH2 or less among light fluxesemitted from the second light source is 0.07 λrms or less.

[0804] Incidentally, in particular,

[0805] it is preferable that a spherical aberration component ofwave-front aberration at a best image point through a transparentsubstrate of the first optical information recording medium for a lightflux whose numerical aperture through an objective lens is NA1 or lessamong light fluxes emitted from the first light source is 0.05 λrms orless.

[0806] When an optical pickup apparatus is made to be one wherein atleast one collimator is provided between the first light source and anobjective lens and between the second light source and an objectivelens, and thereby, each of a light flux entering the objective lens fromthe first light source and a light flux entering the objective lens fromthe second light source is collimated light, adjustment of a pickup iseasy.

[0807] Further, it is possible to reduce cost of an optical pickupapparatus by using one collimator for both light fluxes emittedrespectively from the first light source and the second light source.

[0808] Incidentally, when each of the first light source and the secondlight source is in a separate package, a position of each light sourcecan be set for the collimator so that each light flux may be in parallelwith each other.

[0809] When the first light source and the second light source are inthe same package, it is also possible to make each incident light to anobjective lens to be in parallel with each other by setting thedifference between positions of both light sources in the opticaldirection to be appropriate, or it is also possible, when adjustment isimpossible, to make each incident light to an objective lens to be inparallel with each other by using one wherein chromatic aberration of acollimator is made to be optimum.

[0810] In addition, a light flux entering an objective lens may beeither a converged light flux or a diverged light flux, and by makingthe light flux entering an objective lens from the second light sourceto be higher in terms of divergence than that entering an objective lensfrom the first light source, there is generated under sphericalaberration caused by the difference of divergence, which can reduce anamount of spherical aberration corrected by diffraction pattern.

[0811]FIG. 114 is an illustration wherein numerical aperture NAH2 is thesame as numerical aperture NAL2, and spherical aberration of the lightflux passing through a transparent substrate of the second opticalinformation recording medium (CD) is shown for the light flux emittedfrom the second light source, for the occasion where paraxial chromaticaberration is not corrected and the occasion where paraxial chromaticaberration is corrected (ΔfB=0).

[0812] A converged position of a light flux contributing to reproductionof the second optical information recording medium having NAH2 or lessis at point B when it is not corrected by a diffraction pattern, and itis converged to point A after being corrected by diffraction pattern tocause ΔfB to be almost 0. However, outside the NAH2, no correction ismade by the diffraction pattern, and its aberration shows aberrationcurve S by the refraction surface only.

[0813] As is apparent from the diagram, the gap between the convergingpoint of a light flux and spherical aberration in NAH2 grows greater bycorrection amount ΔfB of paraxial chromatic aberration, and a positionwhere a flare component from NAH2 to NA1 is converged is away greatlyfrom the converging position of the light flux contributing toreproduction of the second optical information recording medium for NAH2or less. Therefore, an influence of the flare component is small on theoptical detector.

[0814] Further, by correcting paraxial chromatic aberration at λ1 andλ2, paraxial chromatic aberration is small even in the vicinity of λ1and λ2, and even when oscillated wavelength is varied by fluctuation oflaser power in the course of recording information on an opticalinformation recording medium, shift of focus is hardly caused, and highspeed recording is possible.

[0815] To make a position where a flare component from NAH2 to NA1 isconverged and the converging position of the light flux for NAH2 or lessto be away from each other, it is possible to obtain the state ofcorrecting aberration shown in FIG. 115, by designing the seconddiffraction pattern so that the second diffraction pattern is arrangedoutside the aforesaid diffraction pattern, thereby, +primary diffractedray of the second diffraction pattern is converged at the aforesaidconverging position for a light flux from the first light source, and alight source from the second light source is transmitted through thesecond diffraction pattern without being diffracted by it.

[0816] Namely, FIG. 115(a) shows the state of correcting aberration forthe light flux emitted from the first light source, wherein aberrationcaused by the diffraction surface established to be relatively large ismade to be no-aberration by the correcting effect of +primary diffractedray for both NAH1 or more and NAH1 or less, and the light flux isconverged at the converging position. However, the light flux passingthrough the diffraction pattern outside NAH2 out of light fluxes emittedfrom the second light source is zero ordered light which is notsubjected to diffraction action, as shown in FIG. 115(b). Therefore, inits state of correcting aberration, aberration which is not subjected tocorrection by the diffraction pattern appears as it is. Accordingly, thegap of the spherical aberration in NAH2 grows greater, and theconverging position of the flare component is away greatly from theconverging position of the light flux contributing to reproduction ofinformation. Therefore, an influence of the flare component is small onthe optical detector.

[0817] The second diffraction pattern may also be designed so that thelight flux from the first light source may not be diffracted by thesecond diffraction pattern, and the light flux from the second lightsource may mainly become −primary diffracted ray. Due to this, whendiffraction-caused spherical aberration of the light flux ranging fromNAH2 to NA1 is exaggerated, spherical aberration through a transparentsubstrate of the second optical information recording medium of thelight flux whose numerical aperture through an objective lens is NAH2 orless can be corrected properly for the second light source, as shown inFIG. 113, and on the other hand, exaggerated spherical aberration of thelight flux outside NAH2 can be made to be greater. As a result, as shownin FIG. 116(b), the gap of the spherical aberration in NAH2 growsgreater, and the converging position of the flare component is awaygreatly from the converging position of the light flux contributing toreproduction of information. Therefore, an influence of the flarecomponent is small on the optical detector.

[0818] In the same way, it is possible to make an influence of flarecomponents to be small, by providing in an optical path from a lightsource to an objective lens an aperture regulating means which transmitsa light flux from the first light source and does not transmit a lightflux passing through an area opposite to an optical axis of the firstdiffraction pattern out of light fluxes from the second light source,and thereby, by reducing flare components reaching an optical detector.

[0819] For the aperture regulating means, a ring-zonal filter whichtransmits the light flux from the first light source and reflects orabsorbs the light flux passing through an area opposite to an opticalaxis of the first diffraction pattern among light fluxes from the secondlight source may be arranged in the optical path after compounding anoutgoing light flux from the first light source and an outgoing lightflux from the second light source with a light compounding means.

[0820] For the filter of this kind, it is possible to use, for example,a dichroic filter employing multiple layers. It is naturally possible tomake either surface of an objective lens to have the filter effectstated above.

[0821] The aperture regulating means may also be a ring-zonal filterwhich transmits a light flux from the first light source and makes thelight flux passing through an area opposite to an optical axis of thediffraction pattern among light fluxes from the second light source tobe diffracted.

[0822] The first optical pickup apparatus—the seventh optical pickupapparatus relating to the eighth embodiment of the invention will beexplained concretely as follows, referring to the drawings.

[0823] The first optical pickup apparatus shown in FIG. 102 has thereinsemiconductor laser 111 representing the first light source forreproduction of the first optical disk and semiconductor laser 112 forreproduction of the second optical disk.

[0824] First, when reproducing the first optical disk, a beam is emittedfrom the first semiconductor laser 111, and the emitted beam istransmitted through beam splitter 190 representing a compounding meansfor beams emitted from both semiconductor lasers 111 and 112, and thenis transmitted through polarized beam splitter 120, collimator 130 and ¼wavelength plate 14 to become a circularly polarized and collimatedlight flux. This light flux is stopped down by aperture 170, and isconverged by objective lens 160 on information recording surface 220through transparent substrate 210 of the first optical disk 200.

[0825] The light flux modulated by information bit and reflected on theinformation recording surface 220 is transmitted again through objectivelens 160, aperture 170, ¼ wavelength plate 140 and collimator 130 toenter polarized beam splitter 120 where the light flux is reflected andis given astigmatism by cylindrical lens 18. Then, the light flux entersoptical detector 300 where signals outputted therefrom are used toobtain signals to read information recorded on the first optical disk200.

[0826] A change in quantity of light caused by changes of a form and aposition of a spot on the optical detector 300 is detected to conductfocusing detection and track detection. Based on this detection,two-dimensional actuator 150 moves objective lens 160 so that a lightflux from the first semiconductor laser 111 may form an image onrecording surface 220 of the first optical disk 200, and moves objectivelens 160 so that a light flux from the semiconductor laser 111 may forman image on a prescribed track.

[0827] When reproducing the second optical disk, a beam is emitted fromthe second semiconductor laser 112, and the emitted beam is reflected onbeam splitter 190 representing a light compounding means, and isconverged on information recording surface 220 through polarized beamsplitter 120, collimator 130, ¼ wavelength plate 140, aperture 170 andobjective lens 160, and through transparent substrate 210 of the secondoptical disk 200, in the same way as that for the light flux from thefirst semiconductor 111.

[0828] The light flux modulated by information bit and reflected on theinformation recording surface 220 enters optical detector 300 againthrough objective lens 160, aperture 170, ¼ wavelength plate 140,collimator 130, polarized beam splitter 120 and cylindrical lens 180,and signals outputted from the optical detector are used to obtainsignals to read information recorded on the second optical disk 200.

[0829] In the same way as in the case of the first optical disk, achange in quantity of light caused by changes of a form and a positionof a spot on optical detector 300 is detected to conduct focusingdetection and track detection, and two-dimensional actuator 150 movesobjective lens 160 for focusing and tracking.

[0830] The second optical pickup apparatus in FIG. 103 has structurewhich is suitable for an optical system for recording and reproduction,and an occasion of reproduction will be explained as follows.Incidentally, in the following example, members which are the same asthose in the optical pickup apparatus in FIG. 102 are given the samesymbols.

[0831] When reproducing the first optical disk, a beam is emitted fromthe first semiconductor laser 111, and the emitted beam is reflected onpolarized beam splitter 121 and is transmitted through collimator 131and ¼ wavelength plate 141 to become circularly polarized and collimatedlight. It is further transmitted through beam splitter 190 representinga light compounding means, then, is stopped down by aperture 170, and isconverged by objective lens 160 on information recording surface 220through transparent substrate 210 of the first optical disk 200.

[0832] The light flux modulated by information bit and reflected oninformation recording surface 220 is transmitted again through beamsplitter 190, ¼ wavelength plate 141 and collimator 131 throughobjective lens 160 and aperture 170 to enter polarized beam splitter 121where astigmatism is given to the light flux when it is transmittedtherethrough. Then, the light flux enters optical detector 301 wheresignals outputted therefrom are used to obtain signals to readinformation recorded on the first optical disk 200.

[0833] A change in quantity of light caused by changes of a form and aposition of a spot on the optical detector 301 is detected to conductfocusing detection and track detection. Based on this detection,two-dimensional actuator 150 moves objective lens 160 so that a lightflux from the first semiconductor laser 111 may form an image onrecording surface 220 of the second optical disk 200, and movesobjective lens 160 so that a light flux from the semiconductor laser 111may form an image on a prescribed track.

[0834] When reproducing the second optical disk, a beam is emitted fromthe second semiconductor laser 112, and the emitted beam is reflected onpolarized beam splitter 122 and is transmitted through collimator 132and ¼ wavelength plate 142 to become circularly polarized and collimatedlight. It is further reflected on beam splitter 190 representing a lightcompounding means, then, is converged by aperture 170 and objective lens160 on information recording surface 220 through transparent substrate210 of the second optical disk 200.

[0835] The light flux modulated by information bit and reflected oninformation recording surface 220 is reflected again on the beamsplitter 190 through objective lens 160 and aperture 170, and istransmitted through ¼ wavelength plate 142 and collimator 132 to enterpolarized beam splitter 122 where astigmatism is given to the light fluxwhen it is transmitted therethrough. Then, the light flux enters opticaldetector 302 where signals outputted therefrom are used to obtainsignals to read information recorded on the second optical disk 200.

[0836] A change in quantity of light caused by changes of a form and aposition of a spot on the optical detector 302 is detected to conductfocusing detection and track detection. Based on this detection,two-dimensional actuator 150 moves objective lens 160 so that a lightflux from the second semiconductor laser 112 may form an image onrecording surface 220 of the first optical disk 200, and moves objectivelens 160 so that a light flux from the semiconductor laser 112 may forman image on a prescribed track, which is the same as the foregoing.

[0837] The third optical pickup apparatus in FIG. 104 has structurewhich is suitable for an optical system for recording and reproduction,and an occasion of reproduction will be explained as follows.

[0838] When reproducing the first optical disk, a beam is emitted fromthe first semiconductor laser 111, and the emitted beam is transmittedthrough coupling lens 60 which makes divergence of diverged lightsource, beam splitter 190 representing a light compounding means andbeam splitter 120, and is further transmitted through collimator 130 and¼ wavelength plate 140 to become circularly polarized and collimatedlight. It is further stopped down by aperture 170 and is converged byobjective lens 160 on information recording surface 220 throughtransparent substrate 210 of the first optical disk 200.

[0839] The light flux modulated by information bit and reflected oninformation recording surface 220 is transmitted again by ¼ wavelengthplate 140 and collimator 130 through objective lens 160 and aperture 170to enter beam splitter 120 where the light flux is reflected and isgiven astigmatism by cylindrical lens 180. Then, the light flux entersoptical detector 301 through concave lens 50, where signals outputtedtherefrom are used to obtain signals to read information recorded on thefirst optical disk 200.

[0840] A change in quantity of light caused by changes of a form and aposition of a spot on the optical detector 301 is detected to conductfocusing detection and track detection. Based on this detection,two-dimensional actuator 150 moves objective lens 160 so that a lightflux from the first semiconductor laser 111 may form an image onrecording surface 220 of the first optical disk 200, and moves objectivelens 160 so that a light flux from the semiconductor laser 111 may forman image on a prescribed track.

[0841] In the second semiconductor laser 112 for reproducing the secondoptical disk, laser/detector accumulating unit 400, optical detector 302and hologram 230 are unitized. “Unit” or “unitization” means thatunitized members and means can be incorporated solidly in an opticalpickup apparatus, and the unit can be incorporated as one part inassembly of an apparatus.

[0842] The light flux emitted from the second semiconductor laser 112 istransmitted through hologram 230, then, is reflected on beam splitter190 representing a light compounding means, and is transmitted throughbeam splitter 120, collimator 130 and ¼ wavelength plate 140 to becomecollimated light. It is further converged on information recordingsurface 220 through aperture 170, objective lens 160 and throughtransparent substrate 210 of the second optical disk 200.

[0843] The light flux modulated by information bit and reflected oninformation recording surface 220 is transmitted again by ¼ wavelengthplate 140 and collimator 130 and beam splitter 120 through objectivelens 160 and aperture 170, then, is reflected on beam splitter 190 andis diffracted by hologram 230 to enter optical detector 302, wheresignals outputted therefrom are used to obtain signals to readinformation recorded on the second optical disk 200.

[0844] Focusing detection and track detection are conducted by detectinga change in a quantity of light caused by the change of form andposition of a spot on optical detector 302, and thereby, objective lens160 is moved by two-dimensional actuator 150 for focusing and tracking.

[0845] When reproducing the first optical disk in the fourth opticalpickup apparatus in FIG. 105 where laser/detector accumulating unit 410,optical detector 301 and hologram 231 are unitized to become the firstsemiconductor laser 111, the light flux emitted from the firstsemiconductor laser 111 passes through the hologram 231, and istransmitted through beam splitter 190 representing a light compoundingmeans and collimator 130 to become a collimated light flux, which isfurther stopped down by aperture 170 to be converged by objective lens160 on information recording surface 220 through transparent substrate210 of the first optical disk 200.

[0846] The light flux which is modulated by information bit andreflected on information recording surface 220 is transmitted bycollimator 130 and beam splitter 190 through objective lens 160 andaperture 170 again, then, is diffracted by hologram 231 to enter opticaldetector 301 where the output signals therefrom are used to obtainreading signals for information recorded on the first optical disk 200.

[0847] Focusing detection and track detection are conducted by detectinga change in a quantity of light caused by the change of form andposition of a spot on optical detector 302, and thereby, objective lens160 is moved by two-dimensional actuator 150 for focusing and tracking.

[0848] When reproducing the second optical disk where laser/detectoraccumulating unit 42, optical detector 302 and hologram 232 are unitizedto become the second semiconductor laser 112, the light flux emittedfrom the second semiconductor laser 112 passes through the hologram 232,and is reflected on beam splitter 190 and is transmitted throughcollimator 130 to become a collimated light flux, which is furtherconverged on information recording surface 220 through objective lens160 and transparent substrate 210 of the second optical disk 200.

[0849] The light flux which is modulated by information bit andreflected on information recording surface 220 is transmitted bycollimator 130 through objective lens 160 and aperture 170 and isreflected on beam splitter 190, then, is diffracted by hologram 232 toenter optical detector 302 where the output signals therefrom are usedto obtain reading signals for information recorded on the second opticaldisk 200.

[0850] Focusing detection and track detection are conducted by detectinga change in a quantity of light caused by the change of form andposition of a spot on optical detector 302, and based on this detection,objective lens 160 is moved by two-dimensional actuator 150 for focusingand tracking.

[0851] In the optical pickup apparatus in FIG. 106, the firstsemiconductor laser 111, the second semiconductor laser 112, opticaldetector 30 and hologram 230 are unitized as laser/detector accumulatedunit 430.

[0852] When reproducing the first optical disk, the light flux emittedfrom the first semiconductor laser 111 is transmitted by hologram 230and collimator 130 to become a collimated light flux, which is furtherstopped down by aperture 170 to be converged by objective lens 160 oninformation recording surface 220 through transparent substrate 210 ofthe first optical disk 200.

[0853] The light flux which is modulated by information bit andreflected on information recording surface 220 is transmitted again bycollimator 130 through objective lens 160 and aperture 170 and isdiffracted by hologram 230 to enter optical detector 300 where theoutput signals therefrom are used to obtain reading signals forinformation recorded on the first optical disk 200.

[0854] Focusing detection and track detection are conducted by detectinga change in a quantity of light caused by the change of form andposition of a spot on optical detector 300, and thereby, objective lens160 is moved by two-dimensional actuator 150 for focusing and tracking.

[0855] When reproducing the second optical disk, the light flux emittedfrom the second semiconductor laser 112 is transmitted by hologram 230and collimator 130 to become mostly a collimated light flux, which isfurther converged on information recording surface 220 through objectivelens 160 and transparent substrate 210 of the second optical disk 200.

[0856] The light flux which is modulated by information bit andreflected on information recording surface 220 is transmitted again bycollimator 130 through objective lens 160 and aperture 170 and isdiffracted by hologram 230 to enter optical detector 300 where theoutput signals therefrom are used to obtain reading signals forinformation recorded on the second optical disk 200.

[0857] Focusing detection and track detection are conducted by detectinga change in a quantity of light caused by the change of form andposition of a spot on optical detector 300, and based on this detection,objective lens 160 is moved by two-dimensional actuator 150 for focusingand tracking.

[0858] In the optical pickup apparatus in FIG. 107, the firstsemiconductor laser 111, the second semiconductor laser 112, the firstoptical detector 301, the second optical detector 302 and hologram 230are unitized as laser/detector accumulated unit 430.

[0859] When reproducing the first optical disk, the light flux emittedfrom the first semiconductor laser 111 is transmitted through thesurface of hologram 230 on the disk side and collimator 130 to become acollimated light flux, which is further stopped down by aperture 170 andis converged by objective lens 160 on information recording surface 220through transparent substrate 210 of the first optical disk 200.

[0860] The light flux which is modulated by information bit andreflected on information recording surface 220 is transmitted again bycollimator 130 through objective lens 160 and aperture 170 and isdiffracted by the surface of hologram 230 on the disk side to enteroptical detector 301 corresponding to the first light source where theoutput signals therefrom are used to obtain reading signals forinformation recorded on the second optical disk 200.

[0861] Focusing detection and track detection are conducted by detectinga change in a quantity of light caused by the change of form andposition of a spot on optical detector 301, and thereby, objective lens160 is moved by two-dimensional actuator 150 for focusing and tracking.

[0862] When reproducing the second optical disk, the light flux emittedfrom the second semiconductor laser 112 is diffracted by the surface ofhologram 230 on the semiconductor laser side and is transmitted throughcollimator 130 to become mostly a collimated light flux. This surface ofhologram 230 on the semiconductor laser side has a function as a lightcompounding means. The light flux is converged on information recordingsurface 220 through aperture 170, objective lens 160 and transparentsubstrate 210 of the second optical disk 200.

[0863] The light flux which is modulated by information bit andreflected on information recording surface 220 is transmitted again bycollimator 130 through objective lens 160 and aperture 170 and isdiffracted by the surface of hologram 230 on the disk side to enteroptical detector 302 corresponding to the second light source where theoutput signals therefrom are used to obtain reading signals forinformation recorded on the second optical disk 200.

[0864] Focusing detection and track detection are conducted by detectinga change in a quantity of light caused by the change of form andposition of a spot on optical detector 302, and based on this detection,objective lens 160 is moved by two-dimensional actuator 150 for focusingand tracking.

[0865] The seventh optical pickup apparatus shown in FIG. 108 is of thestructure which is suitable for an optical system for recording andreproducing, and an occasion of reproduction will be explained asfollows.

[0866] When reproducing the first optical disk, the first semiconductorlaser 111 emits a beam which is transmitted through coupling lens 60which makes divergence of a diverged light source small, beam splitter190 representing a light compounding means and beam splitter 120, and isfurther transmitted through collimator 130 and ¼ wavelength plate 140 tobecome a circularly polarized collimated light. It is further stoppeddown by aperture 170 to be converged by objective lens 160 oninformation recording surface 220 through transparent substrate 210 ofthe first optical disk 200.

[0867] The light flux modulated by information bit and reflected oninformation recording surface 220 is transmitted again by ¼ wavelengthplate 140 and collimator 130 through objective lens 160 and aperture 170to enter beam splitter 120 where the light flux is reflected and isgiven astigmatism by cylindrical lens 180. Then, the light flux entersoptical detector 301 through concave lens 50, and output signalstherefrom are used to obtain reading signals for information recorded onthe first optical disk 200.

[0868] Focusing detection and track detection are conducted by detectinga change in a quantity of light caused by the change of form andposition of a spot on optical detector 301. Then, based on thisdetection, two-dimensional actuator 150 moves objective lens 160 so thata light flux emitted from the first semiconductor laser 111 may form animage on recording surface 220 of the first optical disk 200, and movesobjective lens 160 so that a light flux emitted from the firstsemiconductor laser 111 may form an image on the prescribed track.

[0869] In the second semiconductor laser 112 for reproducing the secondoptical disk, optical detector 302 and hologram 230 are unitized inlaser/detector accumulating unit 400.

[0870] The light flux emitted from the second semiconductor laser 112 istransmitted through hologram 230, then, is reflected on beam splitter190 representing a light compounding means, and is transmitted throughbeam splitter 120, collimator 130 and ¼ wavelength plate 140 to become acollimated light flux. It is further converged on information recordingsurface 220 through transparent substrate 210 of the second optical disk200 through aperture 170 and objective lens 160.

[0871] The light flux modulated by information bit and reflected oninformation recording surface 220 is transmitted again by ¼ wavelengthplate 140, collimator 130 and beam splitter 120 through objective lens160 and aperture 170, then, is reflected on beam splitter 190 and isdiffracted by hologram 230 to enter optical detector 302, where outputsignals therefrom are used to obtain reading signals for informationrecorded on the second optical disk 200.

[0872] Focusing detection and track detection are conducted by detectinga change in a quantity of light caused by the change of form andposition of a spot on optical detector 302, and objective lens 160 ismoved by two-dimensional actuator 150 for focusing and tracking.

[0873] There will be explained the occasion for recording andreproducing the disk of the third Super RENS system which is mostly thesame as the first optical disk in terms of thickness t1 of transparentsubstrate and of necessary numerical aperture NA of the aforesaidobjective lens on the optical information recording medium side which isneeded for recording and reproducing with the first light source havingwavelength of λ1.

[0874] The disk of the third Super RENS system is one which is nowstudied intensively, and an example of its structure is shown in FIG.109. Its recording and reproducing are based on near field optics, andreproduction signals include a system to use reflected light and asystem using transmitted light, and the structure of the present exampleshows a system to obtain reproduction signals by the use of transmittedlight.

[0875] When recording and reproducing the third disk of the Super RENSsystem, the first semiconductor laser 111 emits a beam which istransmitted through coupling lens 60 which makes divergence of divergedlight flux to be small, beam splitter 190 representing a lightcompounding means and beam splitter 120, and is further transmittedthrough collimator 130 and ¼ wavelength plate 140 to become a collimatedlight flux. It is further stopped down by aperture 170, and is convergedby objective lens 160 on non-linear optical film 250 through transparentsubstrate 210 of the first optical disk 200 and first protection film240. On the non-linear optical film 250, there are formed minuteopenings, and energy is transmitted to information recording surface 220on an information recording layer through second protection film 260.Then, the light modulated by information bit and is transmitted throughinformation recording surface 220 is transmitted through protection film270, then, is converged by converging lens 90 which is on the sideopposite to the objective lens, to reach optical detector 305, wherereading signals for information recorded on third optical disk 200 areobtained by the signals outputted from the optical detector.

[0876] On the other hand, the light flux reflected on non-linear opticalfilm 250 is transmitted again by ¼ wavelength plate 140 and collimator130 through objective lens 160 and aperture 170 to enter beam splitter120 where the light flux is reflected and is given astigmatism bycylindrical lens 180 to enter optical detector 301 through concave lens50. Focusing detection and track detection are conducted by detecting achange in a quantity of light caused by the change of form and positionof a spot on optical detector 301. Based on this detection,two-dimensional actuator 150 moves objective lens 160 so that the lightflux emitted from the first semiconductor laser 111 may form an image onnon-linear optical film 250 of the first optical disk, and movesobjective lens 160 so that the light flux emitted from the semiconductorlaser 111 may form an image on the prescribed track.

[0877] When an exclusive objective lens designed so that no-aberrationcollimated light flux may enter from the first light source and anno-aberration spot may be formed through transparent substrate of DVD isused as an objective lens of the aforesaid optical pickup apparatus, andwhen no-aberration collimated light enters the objective lens from thesecond light source and a spot is formed through a transparent substrateof CD, there is generated spherical aberration caused by

[0878] (1) wavelength-dependence of a refractive index of an objectivelens,

[0879] (2) a thickness difference between transparent substrates ofinformation recording media, and

[0880] (3) wavelength-dependence of a refractive index of a transparentsubstrate,

[0881] and most of the spherical aberrations are caused by the aboveitem (2), which has already been stated.

[0882] The spherical aberration caused by the factor of above-mentioneditem (2) is proportional mostly to |t2−t1| and to (NA2)⁴, under thecondition of numerical aperture NA2 which is necessary for recording andreproducing of CD. FIG. 110 shows relationship between image formingmagnification M2 and wave-front aberration for the exclusive lensdesigned to be no-aberration through a transparent substrate of DVD whena collimated light flux having wavelength λ1=650 nm enters an objectivelens, under the conditions that the transparent substrate is the same asCD in terms of thickness, a light source with wavelength λ2=780 nm isused, and the numerical aperture of the light flux emerging from theobjective lens is 0.45. When the image forming magnification M2 is 0, acollimated light flux enters the objective lens, which is the same asDVD.

[0883] In the case of M2=0 as illustrated, spherical aberration of about0.13 λrms is generated, which is greater than 0.07 λrms which isMarechal limit of diffraction limit power. Therefore, it is necessary toset spherical aberration by some means for both DVD and CD so that thewave-front aberration may not be more than Marechal limit.

[0884] When the image forming magnification is made to be negative inthis objective lens, negative spherical aberration is generated in theobjective lens, and it takes the minimum value within the Marechal limitin the case of M ≈−0.06. As stated above, an amount of sphericalaberration which needs to be corrected varies depending on the imageforming magnification, and in the illustrated example, it is notnecessary to correct the spherical aberration with other means in thecase of M≈−0.06. Further, when NA which is necessary for informationrecording of CD-R is 0.5, the spherical aberration to be correctedfurther grows greater.

[0885] Next, there will be explained a preferable collimator adjustingmeans in each optical pickup apparatus stated above. To simplify theexplanation, an optical pickup apparatus employing a light convergingoptical system composed of a collimator and an objective lens will beconsidered. With regard to the distance between the collimator and alight source, when the light source is arranged at the focal point ofthe collimator on its optical axis, a desirable collimated light isemerged from the collimator. Since manufacturing dispersion for the backfocus of the collimator, the distance between the mounting position of asemiconductor laser and a light-emitting point and the housing of theoptical pickup apparatus, is kept to be small, it is possible to obtaina collimated light having accuracy which is not problematic forpractical use, even when the distance between the semiconductor laserand the collimator is not adjusted.

[0886] When recording and/or reproducing two types of opticalinformation recording media each having a transparent substrate withdifferent thickness, by the use of two light sources each havingdifferent wavelength, and when using an objective lens having adiffraction pattern and using the diffracted ray with the same degreeother than zero for each light source, fluctuation of sphericalaberration caused by variation of oscillation wavelength of the laser isgreater, compared with a conventional double aspheric objective lens. Inparticular, in the case of the objective lens in Example 6, wave-frontaberration of 0.001 λms at wavelength of 650 nm is deteriorated to 0.03λrms when the wavelength varies by ±10 nm. What is generated in thiscase is spherical aberration. In the semiconductor laser, there is anindividual difference of oscillation wavelength, and when asemiconductor laser having a large individual difference is used in theoptical pickup apparatus, criteria for spherical aberration of anobjective lens having diffraction pattern become strict, which is aproblem.

[0887] In an objective lens used in an optical pickup apparatus, when anincident light flux is changed from collimated light to diverged light,negative 3-ordered spherical aberration is increased, and when it ischanged from collimated light to converged light, positive 3-orderedspherical aberration is increased, thus, it is possible to control3-ordered spherical aberration by changing divergence of an incidentlight flux to the objective lens. In the objective lens as in Example 6,main components of spherical aberration caused by the individualdifference in oscillated wavelength of the semiconductor laser are3-ordered spherical aberration, thus, it is possible to make 3-orderedspherical aberration of the total light converging optical system to bethe designed value, by changing divergence of an incident light flux tothe objective lens.

[0888] Incidentally, when there is a coupling lens such as a collimatorin a light converging optical system, it is possible to control the3-ordered spherical aberration of an objective lens by moving thecoupling lens in the direction of its optical axis. Further, when thereis a coupling lens such as a collimator, the same object as in theforegoing can be attained by moving a semiconductor laser in thedirection of the optical axis. The semiconductor laser may naturally bemoved in the optical axis direction even when a coupling lens such as acollimator exists.

Example 19

[0889] As concrete examples of an objective lens related to the 8thembodiment, Example 19 of spherical-aberration-corrected lens is shownin FIG. 111, Table 20 and Table 21 as follows.

[0890] In Table 20, ri represents a radius of curvature of therefraction surface, each of di and di′ represents a distance betweensurfaces, and each of ni and ni′ represent the refractive index at mainwavelength. Further, the expression for surface form is shown below.$\begin{matrix}{X = {\frac{h^{2}/r}{1 + \sqrt{1 - {( {1 + \kappa} )( {h/r} )^{2}}}} + {\sum\limits_{j}\quad {A_{j}h^{p\quad j}}}}} & \quad\end{matrix}$

[0891] In the expression, X represents an axis in the direction of theoptical axis, h represents an axis in the direction perpendicular to theoptical axis, the direction for advancement of light is positive, rrepresents a paraxial radius of curvature, κ represents constant of thecone, Aj represents aspheric surface coefficient, and Pj (Pi≧3)represents aspheric surface power number.

[0892] The diffraction surface is as shown in Expression 1 as a functionof an optical path difference. The unit is in mm. TABLE 20 Wavelength635 nm 780 nm Focal distance 3.370 3.397 Aperture diameter Φ 4.04 mmLateral magnification of objective lens 0 Surface No. ri di di′ ni ni′ 1∞ 2 2.131 2.6 1.5300 1.5255 3 −6.373 1.5657 1.2052 4 ∞ 0.6 1.2 1.57871.5709 5 ∞

[0893] Both di and ni represent values for the first optical informationrecording medium (t1=0.6 mm).

[0894] Both di′ and ni′ represent values for the second opticalinformation recording medium (t2=1.2 mm). TABLE 21 Second First split 0≦ H ≦ 1.6984 surface surface κ = −3.6612 × 10⁻² (Aspheric A₁ = −3.2000 ×10⁻³ P1 = 4.0 surface A₂ = −9.5500 × 10⁻⁴ P2 = 6.0 coefficient) A₃ =9.4224 × 10⁻⁵ P3 = 8.0 A₄ = −2.8750 × 10⁻⁵ P4 = 10.0 (Diffraction B₂ = 0surface B₄ = −8.3027 × 10⁻⁴ coefficient) B₆ = −1.6462 × 10⁻⁴ B₈ = 1.3105× 10⁻⁵ Second split 1.6984 ≦ H surface κ = −9.8006 × 10⁻¹ (Aspheric A₁ =6.0790 × 10⁻³ P1 = 4.0 surface A₂ = 2.8149 × 10⁻⁴ P2 = 6.0 coefficient)A₃ = 6.6735 × 10⁻⁶ P3 = 8.0 A₄ = −2.8790 × 10⁻⁶ P4 = 10.0 Third Asphericκ = −2.4934 × 10 surface surface A₁ = 9.6641 × 10⁻³ P1 = 4.0 coefficientA₂ = −3.7568 × 10⁻³ P2 = 6.0 A₃ = 7.9367 × 10⁻⁴ P3 = 8.0 A₄ = 7.3523 ×10⁻⁵ P4 = 10.0

[0895] A sectional view of the lens in the aforesaid example is shown inFIG. 111, and its spherical aberration diagram is shown in FIG. 112. InFIG. 111, portion S2 d including an optical axis of the second surfaceS2 has a diffraction pattern, and portion S2 r outside thereof is anaspheric surface refraction surface. FIG. 112(a) shows a sphericalaberration diagram at wavelength of 635 nm and first optical informationrecording medium (t1=0.6 mm), which is sufficiently corrected in termsof aberration. FIG. 112(b) shows a spherical aberration diagram atwavelength of 780 nm and second optical information recording medium(t2=1.2 mm), wherein a light flux passing through the first splitsurface S2 d is corrected in terms of spherical aberration by an effectof diffraction, and a light flux passing through second split surface S2r becomes flare light and has an effect which is the same as that of anaperture.

[0896] The lens in the aforesaid example is an objective lens withNAH2=0.5 and NAL2=0. The diffraction pattern section of this lensbecomes a pattern on a annular band whose center is an optical axis, andits step number is about 13. A boundary between a circumferentialsection of the diffraction pattern which is farthest from the opticalaxis and the refraction surface has a step of about 21 μm.

[0897] In the case of NAH2=0.45, the number of steps of the diffractionpattern is about 9, and an amount of the step is about 13 μm. An amountof the step and the number of steps of the diffraction pattern areroughly proportional to the fourth power of NAH2.

[0898] In the case of NAL2=0 as in the aforesaid example, the number ofsteps of the diffraction pattern is increased in proportional tospherical aberration to be corrected.

[0899] In the objective lens in the invention, satisfactory effects canbe obtained even when the depth of the diffraction pattern in thedirection of an optical axis is 2 μm or less. However, when the numberof steps of the diffraction pattern is large, it is difficult to processthe metal mold and to mold. thus, it is desirable that the number ofsteps is as small as possible.

[0900] This can be attained by the following.

[0901] (1) An image forming magnification for CD is made to be slightlysmaller than that for DVD, and an amount of spherical aberration to becorrected is made to be small in advance. It is preferable that mCD(magnification for recording and reproducing of CD)-mDVD (magnificationfor recording and reproducing of DVD) is in a range of −{fraction(1/15)}-0.

[0902] (2) A diffraction pattern is not provided on the portion wherethe depth is great and the numerical aperture is small.

[0903] For example, if image forming magnification of DVD is made to be0, and image forming magnification of CD is made to be −0.03, thespherical aberration to be corrected is halved, and even when NAH2 ismade to be 0.5 for covering CD-R, the number of steps is about 7 and anamount of a step is about 11 μm.

[0904] When an amount of step is small, the shape of step S2 s may alsobe one which flows smoothly from diffraction pattern section S2 d torefraction surface section S2 r.

[0905] When image forming magnification for both DVD and CD is 0, ifNAL2 is made to be 0.36, residual spherical aberration component WSA(NAL2) of the wave-front aberration of a light flux whose numericalaperture is not more than NAL2 is about 0.053 λrms. By providing theoptimum diffraction pattern to this, it is possible to make the RMSvalue of the wave-front aberration up to NAH2 to be small, while keepingthe wave-front aberration of DVD to 0.

[0906] Residual spherical aberration component WSA (NAH2) of thewave-front aberration of a light flux whose numerical aperture is notmore than NAH2 can be approximated by the following expression.

WSA(NAH@)=(NAL2/NAH2)2×WSA(NAL2)

[0907] Therefore, the aforesaid value is 0.034 λrms for NAH2=0.45, andit is 0.027 λrms for NAH2=0.5, which are sufficiently smaller than theMarechal limit value.

[0908] In this case, excessive spherical aberration is generated forNAL2 or less. Therefore, the spherical aberration from NAL2 to NAH2 isnot made to be zero, but it can be made to agree with the best focus ofthe light flux of NAL2 or less. Since this best focus position is at theposition exceeding the paraxial focus point, the spherical aberration tobe corrected by the diffraction pattern can be small. Further, for thelight flux for NAL2 or less, the diffraction pattern is not necessary.Due to these two effects, the number of steps of the diffraction patternin the case of NAH2=0.5 can be about 6, and the number of steps of thediffraction pattern in the case of NAH2=0.45 can be 4.

[0909] It is naturally possible to make the diffraction pattern to besmaller by making image forming magnification of CD to be smaller thanthat of DVD, and the minimum of two steps makes interchangeablereproduction for DVD and CD possible.

[0910] Incidentally, there is proposed a high density opticalinformation recording medium whose transparent substrate has a thicknessof 0.1 mm. For recording and reproduction for this, a blue semiconductorlaser is used, a two-element objective lens is used, and 0.85 is neededas NA1. On the other hand, CD-RW employs a light source wherein athickness of a transparent substrate is 1.2 mm and a wavelength is 780,and NA2 is made to be 0.55. In this interchangeable optical system, anamount of correction of spherical aberration is 2.7 times greater,because NA2 is large and t1-t2 is also large, compared with DVD and CD-R(NAH2=0.5). Therefore, the number of steps of the diffraction pattern isabout 35.

[0911] For further correction of paraxial chromatic aberration, thenumber of steps of the diffraction pattern is increased. For thecorrection including paraxial chromatic aberration up to NA1, hundredsof steps are needed. In such a case, it is also possible to providediffraction pattern to plural optical surfaces.

[0912] A certain portion within a range from NAL2 to NAH2 may also bemade a refraction surface, when necessary.

[0913] Further, in the case of t1>t2, −first ordered light is usedbecause a sign of the generated spherical aberration is reversed.

[0914] Equally, even in the case of DVD and CD, image formingmagnification of an objective lens for CD is fairly smaller than thatfor DVD, and when under spherical aberration remains, −first orderedlight is used equally.

[0915] Incidentally, with regard to DVD and CD which represent a matterof primary concern currently, there is shown an example to execute witha single objective lens by using two lasers each having differentrecording or wavelength. As stated already, when assuming that λ1represents a wavelength of the first light source and λ2 (λ2>λ1)represents a wavelength of the second light source, there is introducedthe first diffraction pattern wherein +first ordered diffracted ray isused in the case of t1<t2, and −first ordered diffracted ray is used inthe case of t1>t2, and the former is applied to DVD (using the firstlight source) and CD (using the second light source).

[0916] There have recently been put to practical use various lightsources each having a different wavelength such as a blue semiconductorlaser and an SHG laser, and it is estimated that lots of new opticalinformation recording media will further appear on the market. In thiscase, though the necessary spot size is determined from the recordingdensity of the optical information recording medium, NA which isnecessary for recording or recording/reproduction varies dependent on awavelength of the light source to be used. Therefore, each of thethickness of a transparent substrate of an optical information recordingmedium and of the necessary NA is classified into the following fourcases, for two optical information recording media.

(1) t1<t2, NA1>NA2

(2) t1<t2, NA1<NA2

(3) t1>t2, NA1>NA2

(3) t1>t2, NA1<NA2

[0917] In the aforesaid explanation, there have especially beenexplained in detail various items such as the number of ordered ofdiffraction of the first diffraction pattern used in the case (1) abovefor each light source, a range (NAH1, NAL1, NAH2 and NAL2), types and NAranges of a light source wherein a diffraction pattern section and atransparent section are required to be converged at the same position, arange of NA setting spherical aberration for each light source, a rangeof NA wherein wave-front aberration for each light source is required tobe 0.07 λrms or less, necessity to make the number of ordered ofdiffraction of the second diffraction pattern for each light source andthe first diffraction pattern to be converged at the same position, andconditions for restricting a light flux from which light source in thecase of introducing the aperture restriction. Detailed explanation foreach of (2), (3) and (4) cases is omitted here, because they can beexecuted easily from the detailed description of (1).

[0918] For manufacturing of lenses, it is also possible either to moldplastic materials or glass materials solidly by the use of a metal moldin which the diffraction pattern is engraved, or to form, on the basematerial of glass or plastic, an optical surface including thediffraction pattern of the invention, by the use of UV-setting resins.It is further possible to manufacture through coating or directprocessing.

[0919] As stated above, it is also possible to arrange so that theoptical surface having the effect of the invention is provided on anoptical element which is separate from an objective lens, and theoptical surface is provided on the side of the objective lens closer toa light source or on the side closer to an optical information recordingmedium. It can also be provided naturally on an optical surface of acollimator or a light compounding means through which a light flux fromthe first light source and that from the second light source pass.However, an amount of tracking is restricted, because an optical axis ofthe diffraction pattern and that of the objective lens move relativelywhen the objective lens is moved for tracking.

[0920] Though the diffraction pattern is made to be in a form of aconcentric circle which is concentric with an optical axis, forconvenience' sake of explanation, the invention is not limited to this.

[0921] Though the objective lens shown concretely in Examples 1-19 iscomposed of a single lens as an example, the objective lens may also becomposed of plural lenses, and an occasion wherein at least one surfaceof the plural lenses has the diffraction surface of the invention isincluded in the invention.

[0922] In the invention, selective generation of diffracted ray withspecific number of ordered means that diffraction efficiency of thediffracted ray with the specific number of ordered is higher than thatof each diffracted ray with number of ordered other than the specificnumber of ordered, for light with a prescribed wavelength, which hasalready been stated. It is preferable that, for rays of light having twowavelengths which are different from each other, diffraction efficiencyof diffracted ray with a specific number of ordered is higher by 10% ormore than that of each diffracted ray with another number of ordered,and it is more preferable that the efficiency is higher by 30% or more,while, the diffraction efficiency of 50% or more of the diffracted raywith the specific number of ordered is preferable, and the morepreferable is 70% or more which lessen the loss of a quantity of lightand is preferable from the viewpoint of practical use.

[0923] With regard to the diffraction surface of the invention, it ispreferable that existence of the diffraction surface improves sphericalaberration, compared with an occasion of no diffraction surface, namelyan occasion where the surface enveloping the relief of the diffractionsurface is simulated to be assumed, when diffraction rays of lightgenerated selectively and have at least two wavelengths which aredifferent from each other are focused respectively, as shown in theaforesaid embodiment and in the concrete examples of the lens.

[0924] Further, in the invention, it is preferable, from the viewpointof obtaining a desirable spot which is effective on a practical use,that wave-front aberration of the diffracted ray with specific number ofordered generated selectively for each (wavelength λ) of rays of lighthaving at least two wavelengths which are different from each other is0.07 λrms.

[0925] As stated above, the invention makes it possible to obtain anoptical system with simple structure employing at least one opticalelement having a diffraction surface wherein spherical aberration andaxial chromatic aberration can be corrected for rays of light having atleast two wavelengths which are different from each other, an opticalpickup apparatus, a recording and reproducing apparatus, a lens, anoptical element, a diffraction optical system for optical disks, arecording and/or reproducing apparatus for a sound and/or an image, andan objective lens. It is further possible to make an optical system tobe small in size, light in weight and low in cost. When the opticalelement has a diffraction surface which makes the diffraction efficiencyof the diffracted ray having the same number of ordered to be maximumfor rays of light having at least two wavelengths which are differentfrom each other, a loss of a quantity of light can be lessened, comparedwith an occasion where the diffraction efficiency of the diffracted rayof the diffraction surface having a different number of ordered is madeto be maximum.

[0926] With regard to the inventions described in Items 72-88, inparticular, it is possible, by providing a diffraction lens on thediffraction surface, to obtain a diffraction optical system wherein anoptical system for recording and reproducing having two light sourceseach having a different wavelength is used, a loss of a quantity oflight for each light source wavelength is little, and aberration can becorrected up to almost the diffraction limit.

[0927] With regard to the inventions described in Items 89-98, inparticular, it is possible to conduct recording of information and/orreproducing of information for different optical disk with one objectivelens, for three light sources each having a different wavelength, anoptical pickup apparatus can be made thinner, and a problem of high costcan be solved, as stated above.

[0928] With regard to the inventions described in Items 99-112, inparticular, it is possible to provide an optical pickup apparatus and anobjective lens wherein spherical aberration caused by a difference ofthickness of a transparent substrate, chromatic aberration of sphericalaberration generated by a difference of wavelength and axial chromaticaberration are corrected, by designing an aspheric surface coefficientand a coefficient of a phase difference function properly, in an opticalpickup apparatus having three light sources each having a differentwavelength.

[0929] With regard to the inventions described in Items 113-181, inparticular, it is possible to provide a spherical-aberration-correctedobjective lens for recording and reproducing an optical informationrecording medium and an optical pickup apparatus wherein recording andreproducing can be conducted by light fluxes having differentwavelengths and by a single light converging optical system, for opticalinformation recording medium having a transparent substrate with adifferent thickness, by providing plural split surfaces on the objectivelens and thereby by arranging the diffraction surface on the first splitsurface.

[0930] In addition, an objective lens for an optical pickup apparatus iscomposed of plural annular bands split to be in a form of a concentriccircle, and each annular band is corrected in terms of aberration up tothe diffraction limit mostly, for plural light sources each having adifferent wavelength and for transparent substrates each having adifferent thickness of a recording surface, thus, flare light enteringan optical detector is reduced, and manufacturing of the objective lensis easy. “disclosed embodiment can be varied by a skilled person withoutdeparting from the spirit and scope of the invention”

What is claimed is:
 1. An optical pickup apparatus for reproducinginformation from an optical information recording medium or forrecording information onto an optical information recording medium,comprising: a first light source for emitting first light flux having afirst wavelength; a second light source for emitting second light fluxhaving a second wavelength, the first wavelength being different fromthe second wavelength; a converging optical system having an opticalaxis and a diffractive portion, and a photo detector; wherein in casethat the first light flux passes through the diffractive portion togenerate at least one diffracted ray, an amount of n-th ordereddiffracted ray of the first light flux is greater than that of any otherordered diffracted ray of the first light flux, and in case that thesecond light flux passes through the diffractive portion to generate atleast one diffracted ray, an amount of n-th ordered diffracted ray ofthe second light flux is greater than that of any other ordereddiffracted ray of the second light flux, where n stands for an integerother than zero.
 2. The optical pickup apparatus of claim 1, wherein theoptical pickup apparatus reproduces information from at least two kindsof optical information recording media or records information onto atleast two kinds of optical information recording media, and wherein thefirst light source emits the first light flux for reproducinginformation from a first optical information recording medium or forrecording information onto a first optical information recording medium;and the second light source emits the second the light flux forreproducing information from a second optical information recordingmedium or for recording information onto a second optical informationrecording medium.
 3. The optical pickup apparatus of claim 2, whereinthe converging optical system is capable of converging the n-th ordereddiffracted ray of the first light flux, which is generated at thediffractive portion by the first light flux being reached thediffractive portion, on a first information recording plane of the firstoptical information recording medium through a first transparentsubstrate so as to reproduce information recorded on the first opticalinformation recording medium or to record information onto the firstoptical information recording medium, wherein the converging opticalsystem is capable of converging the n-th ordered diffracted ray of thesecond light flux, which is generated at the diffractive portion by thesecond light flux being reached the diffractive portion, on a secondinformation recording plane of the second optical information recordingmedium through a second transparent substrate so as to reproduceinformation recorded on the second optical information recording mediumor to record information onto the second optical information recordingmedium, and wherein the photo detector is capable of receiving lightflux reflected from the first information recording plane or the secondinformation recording plane.
 4. The optical pickup apparatus of claim 3,wherein the converging optical system comprises an objective lens,wherein the converging optical system is capable of converging the n-thordered diffracted ray of the first light flux on the first informationrecording plane of the first optical information recording medium on acondition that a wave-front aberration is not larger than 0.07 λrms whena numerical aperture at an image side of the objective is within apredetermined numerical aperture of the first optical informationrecording medium, and wherein the converging optical system is capableof converging the n-th ordered diffracted ray of the second light fluxon the second information recording plane of the second opticalinformation recording medium on a condition that a wave-front aberrationof the second light flux is not larger than 0.07 λrms when a numericalaperture at the image side of the objective is within a predeterminednumerical aperture of the second optical information recording medium.5. The optical pickup apparatus of claim 2, wherein the first opticalinformation recording medium has a first transparent substrate ofthickness t1, and wherein the second optical information recordingmedium has a second transparent substrate of thickness t2, wherein thethickness t2 is different from the thickness t1.
 6. The optical pickupapparatus of claim 5, wherein the converging optical system comprises anobjective lens, wherein the converging optical system is capable ofconverging the n-th ordered diffracted ray of the first light flux on afirst information recording plane of the first optical informationrecording medium on a condition that a wave-front aberration is notlarger than 0.07 λrms when a numerical aperture at an image side of theobjective is within a predetermined numerical aperture of the firstoptical information recording medium, and wherein the converging opticalsystem is capable of converging the n-th ordered diffracted ray of thesecond light flux on a second information recording plane of the secondoptical information recording medium on a condition that a wave-frontaberration is not larger than 0.07 λrms when a numerical aperture at animage side of the objective is within a predetermined numerical apertureof the second optical information recording medium.
 7. The opticalpickup apparatus of claim 5, wherein the following formula is satisfied:λ1>λ2 and t1<t2 where λ1 is the wave length of the first light flux, λ2is the wave length of the second light flux, t1 is the thickness of thefirst transparent substrate, and t2 is the thickness of the secondtransparent substrate.
 8. The optical pickup apparatus of claim 7,wherein the following formula is satisfied: NA1>NA2 Where NA1 is apredetermined numerical aperture of the first optical informationrecording medium for the first light flux at an image side of theobjective lens, and NA2 is a predetermined numerical aperture of thesecond optical information recording medium for the second light flux atan image side of the objective lens.
 9. The optical pickup apparatus ofclaim 8, wherein the n-th ordered diffracted ray is a positive firstordered diffracted ray.
 10. The optical pickup apparatus of claim 8,wherein the following formula is satisfied: 0.55 mm<t1<0.65 mm 1.1mm<t2<1.3 mm 630 nm<λ1<670 nm 760 nm<λ2<820 nm 0.55<NA1<0.680.40<NA2<0.55
 11. The optical pickup apparatus of claim 10, wherein theconversion optical system comprises an objective lens, the objectivelens has a diffractive portion, λ1=650 nm, t1=0.6 mm, and NA=0.6, andwherein in case that the first light flux which is composed of parallelrays and have a uniform intensity distribution are introduced in theobjective lens and are converged on the first information recordingplane through the first transparent substrate, a diameter of convergedspot is 0.88 μm to 0.91 μm at the best focusing condition.
 12. Theoptical pickup apparatus of claim 10, wherein the conversion opticalsystem comprises an objective lens, the objective lens has a diffractiveportion, λ1=650 nm, t1=0.6 mm, and NA1=0.65 and wherein in case that thefirst light flux which is composed of parallel rays and have a uniformintensity distribution are introduced in the objective lens and areconverged on the first information recording plane through the firsttransparent substrate, a diameter of converged spot is 0.81 μm to 0.84μm at the best focusing condition.
 13. The optical pickup apparatus ofclaim 10, wherein t1 is 0.6 mm, t2 is 1.2 mm, λ1 is 650 nm, λ2 is 780nm, NA1 is 0.6 and NA2 is 0.45.
 14. The optical pickup apparatus ofclaim 8, wherein the conversion optical system comprises an objectivelens, and the objective lens has a diffractive portion, and wherein incase that the converging optical system converges the n-th ordereddiffracted ray of the second light flux on the second informationrecording plane of the second optical information recording medium, thespherical aberration comprises at least a discontinuing section by oneplace.
 15. The optical pickup apparatus of claim 14, wherein thespherical aberration comprises the discontinuing section at a place nearNA2.
 16. The optical pickup apparatus of claim 14, wherein the sphericalaberration comprises the discontinuing section at a place at which NA is0.45.
 17. The optical pickup apparatus of claim 14, wherein thespherical aberration comprises the discontinuing section at a place atwhich NA is 0.5.
 18. The optical pickup apparatus of claim 14, whereinthe converging optical system converges the n-th ordered diffracted rayhaving a numerical aperture smaller than NA1 in the first light fluxhaving passed over the diffractive portion on the first informationrecording plane of the first recording medium such that the wave-frontaberration at the best image point is 0.07 λrms and the convergingoptical system converges the n-th ordered diffracted ray having anumerical aperture smaller than that of the discontinuing section in thesecond light flux having passed over the diffractive portion on thesecond information recording plane of the second recording medium suchthat the wave-front aberration at the best image point is 0.07 λrms. 19.The optical pickup apparatus of claim 8, wherein the conversion opticalsystem comprises an objective lens, and the objective lens has adiffractive portion, in case that the converging optical systemconverges the n-th ordered diffracted ray of the second light fluxhaving passed over the diffractive portion on the second informationrecording plane of the second optical information recording medium inorder to conduct the recording or the reproducing for the second opticalinformation recording medium, the spherical aberration is continuedwithout having a discontinuing section.
 20. The optical pickup apparatusof claim 19, wherein the spherical aberration at NA1 is not smaller than20 μm and the spherical aberration at NA2 is not larger than 10 μm. 21.The optical pickup apparatus of claim 5, wherein the following formulais satisfied: λ1<λ2 and t1>t2 where λ1 is the wave length (nm) of thefirst light flux, λ2 is the wave length (nm) of the second light flux,t1 is the thickness (mm) of the first transparent substrate, and t2 isthe thickness (mm) of the second transparent substrate.
 22. The opticalpickup apparatus of claim 21, wherein the n-th ordered diffracted ray isa negative first ordered diffracted/ray.
 23. The optical pickupapparatus of claim 1, wherein a diffracting efficiency at thediffractive portion for the n-th ordered diffracted ray of the firstlight flux is A% and a diffracting efficiency for another ordereddiffracted ray of the first light flux is B%, the diffractingefficiencies satisfy the following formula: A−B≧10, and a diffractingefficiency at the diffractive portion for the n-th ordered diffractedray of the second light flux is A′% and a diffracting efficiency foranother ordered diffracted ray of the first light flux is B′%, thediffracting efficiencies satisfy the following formula: A′−B′≧10. 24.The optical pickup apparatus of claim 1, wherein a diffractingefficiency at the diffractive portion for the n-th ordered diffractedray of the first light flux is A% and a diffracting efficiency foranother ordered diffracted ray of the first light flux is B%, thediffracting efficiencies satisfy the following formula: A−B≧50, and adiffracting efficiency at the diffractive portion for the n-th ordereddiffracted ray of the second light flux is A′% and a diffractingefficiency for another ordered diffracted ray of the first light flux isB′%, the diffracting efficiencies satisfy the following formula:A′−B′≧50.
 25. The optical pickup apparatus of claim 1, wherein adifference in wavelength between the first light flux and the secondlight flux is 80 nm to 400 nm.
 26. The optical pickup apparatus of claim1, wherein the diffractive portion comprises a plurality of annularbands formed coaxially around the optical axis or around a point nearthe optical axis as a center.
 27. The optical pickup apparatus of claim26, wherein a phase difference function expressed by power seriesindicating each position of the plurality of annular bands has acoefficient except zero in at least one term except 2nd power term. 28.The optical pickup apparatus of claim 26, wherein a phase differencefunction expressed by power series indicating each position of theplurality of annular bands has a coefficient except zero in 2nd powerterm.
 29. The optical pickup apparatus of claim 26, wherein a phasedifference function expressed by power series indicating each positionof the plurality of annular bands has not 2nd power term.
 30. Theoptical pickup apparatus of claim 26, wherein a sign of negative orpositive of a diffracting effect added by the diffractive portion isswitched at least one time in a direction departing from the opticalaxis perpendicularly to the optical axis.
 31. The optical pickupapparatus of claim 30, wherein the plurality of annular bands in thediffractive portion are blazed, a stepped section in an annular bandlocated at a side close to the optical axis is located at a side distantfrom the optical axis, and a stepped section in an annular band locatedat a side distant from the optical axis is located at a side close tothe optical axis.
 32. The optical pickup apparatus of claim 30, whereinthe plurality of annular bands in the diffractive portion are blazed, astepped section in an annular band located at a side close to theoptical axis is located at a side close to the optical axis, and astepped section in an annular band located at a side distant from theoptical axis is located at a side distant from the optical axis.
 33. Theoptical pickup apparatus of claim 26, wherein the converging opticalsystem comprises an objective lens, a pitch Pf of the annular bands inthe diffractive portion corresponding to a maximum numerical aperture atthe image side of the objective lens and a pitch Ph of the annular bandsin the diffractive portion corresponding to half of the maximumnumerical aperture satisfy the following formula. 0.4≦|(Ph/Pf)−2|≦25 34.The optical pickup apparatus of claim 26, wherein the diffractiveportion comprises a first diffractive pattern and a second diffractivepattern and the second diffractive pattern is located distant from theoptical axis more than the first diffractive pattern.
 35. The opticalpickup apparatus of claim 34, wherein the amount of n-th ordereddiffracted ray is generated more than that of other ordered diffractedray in the first light flux having passed over the first diffractivepattern of the diffractive portion, the amount of the n-th ordereddiffracted ray is generated more than that of other ordered diffractedray in the second light flux having passed over the first diffractivepattern of the diffractive portion, an amount of the n-th ordereddiffracted ray is generated more than that of other ordered diffractedray in the first light flux having passed over the second diffractivepattern of the diffractive portion, and an amount of 0th ordereddiffracted ray is generated more than that of other ordered diffractedray in the second light flux having passed over the second diffractivepattern of the diffractive portion.
 36. The optical pickup apparatus ofclaim 34, wherein an amount of n-th ordered diffracted ray is generatedmore than that of other ordered diffracted ray in the first light fluxhaving passed over the first diffractive pattern of the diffractiveportion, an amount of the 0th ordered diffracted ray is generated morethan that of other ordered diffracted ray in the second light fluxhaving passed over the first diffractive pattern of the diffractiveportion, an amount of the n-th ordered diffracted ray is generated morethan that of other ordered diffracted ray in the first light flux havingpassed over the second diffractive pattern of the diffractive portion,and an amount of negative ordered diffracted ray except the n-th orderis generated more than that of other ordered diffracted ray in thesecond light flux having passed over the second diffractive pattern ofthe diffractive portion.
 37. The optical pickup apparatus of claim 26,wherein the converging optical system comprises an objective lens, alllight flux within the maximum numerical aperture at an image side of theobjective lens, passes through the diffractive portion.
 38. The opticalpickup apparatus of claim 26, wherein the converging optical systemcomprises an objective lens, a part of light flux within the maximumnumerical aperture at an image side of the objective lens, passesthrough the diffractive portion and another part of light flux withinthe maximum numerical aperture does not pass through the diffractiveportion.
 39. The optical pickup apparatus of claim 26, wherein a numberof steps on the annular bands in the diffractive portion is 2 to
 45. 40.The optical pickup apparatus of claim 39, wherein a number of steps onthe annular bands in the diffractive portion is 2 to
 15. 41. The opticalpickup apparatus of claim 26, wherein a depth, in the optical axialdirection, of a stepped section on the annular bands in the diffractiveportion is not larger than 2 μm.
 42. The optical pickup apparatus ofclaim 26, wherein the optical converging system comprises an objectivelens and the diffractive portion is provided on the objective lens, thepitch of the diffractive portion at a point at which NA=0.4 is 10 μm to70 μm.
 43. The optical pickup apparatus of claim 1, wherein theconverging optical system comprises a lens having a refracting surfaceand wherein the diffractive portion is provided on the lens.
 44. Theoptical pickup apparatus of claim 43, wherein the lens provided with thediffractive portion is an objective lens.
 45. The optical pickupapparatus of claim 44, wherein the objective lens provided with thediffractive portion comprises a flange section on a outer circumferencethereof.
 46. The optical pickup apparatus of claim 44, wherein therefracting surface of the objective lens provided with the diffractiveportion is an aspherical surface.
 47. The optical pickup apparatus ofclaim 43, wherein the lens provided with the diffractive portion is madeof a material whose Abbe's number νd is not smaller than
 50. 48. Theoptical pickup apparatus of claim 43, wherein the lens provided with thediffractive portion is a plastic lens.
 49. The optical pickup apparatusof claim 43, wherein the lens provided with the diffractive portion is aglass lens.
 50. The optical pickup apparatus of claim 1, wherein then-th ordered diffracted ray is a positive first ordered diffracted rayor a negative first ordered diffracted ray.
 51. The optical pickupapparatus of claim 1, wherein a diffracting efficiency of the n-thordered diffracted ray by the diffractive portion becomes maximum in awavelength between the wavelength of the first light flux and thewavelength of the second light flux.
 52. The optical pickup apparatus ofclaim 1, wherein a diffracting efficiency of the n-th ordered diffractedray by the diffractive portion becomes maximum in the wavelength of thefirst light flux or in the wavelength of the second light flux.
 53. Theoptical pickup apparatus of claim 1, wherein the converging opticalsystem comprises an objective lens, the wavelength of the second lightflux is longer than the wavelength of the first light flux, and an axialchromatic aberration Z satisfies the following formula: −λ₂/(2NA ₂²)≦Z≦λ₂/(2NA ₂ ²) where λ₂ is the wavelength of the second light flux,and NA₂ is a predetermined numerical aperture at an image side of theobjective lens of the second optical information recording medium forthe second light flux.
 54. The optical pickup apparatus of claim 1,further comprising: a third light source for emitting third light fluxhaving a third wavelength, wherein the third wavelength is differentfrom the first wavelength and the second wavelength.
 55. The opticalpickup apparatus of claim 54, wherein an amount of n-th ordereddiffracted ray is generated greater than that of other ordered ofdiffracted ray in the third light flux having passed over thediffractive portion.
 56. The optical pickup apparatus of claim 1,wherein the converging optical system comprises an objective lens, andat least one of an aperture limiting means to shade or diffract thefirst light flux positioned outside of the predetermined numericalaperture of the second optical information recording medium at the imageside of the objective lens and to allow the second light flux to passthrough and an aperture limiting means to shade or diffract the secondlight flux positioned outside of the predetermined numerical aperture ofthe first optical information recording medium at the image side of theobjective lens and to allow the first light flux to pass through. 57.The optical pickup apparatus of claim 1, wherein the converging opticalsystem comprises an objective lens, and dose not comprise an aperturelimiting means to shade or diffract the first light flux positionedoutside of the predetermined numerical aperture of the second opticalinformation recording medium at the image side of the objective lens andto allow the second light flux to pass through and an aperture of thefirst optical information recording medium limiting means to shade ordiffract the second light flux positioned outside of the predeterminednumerical aperture at the image side of the objective lens and to allowthe first light flux to pass through.
 58. The optical pickup apparatusof claim 1, wherein the converging optical system comprises a lenshaving a refracting surface and wherein the diffractive portion isprovided on the lens and the following formula is satisfied: −0.0002/°C.<Δn/ΔT<−0.00005° C. 0.05 nm/° C.<Δλ ₁ /ΔT<0.5 nm/° C. wherein ΔT is atemperature change, and Δn is a change in refractive index of the lens.Δλ₁ is a change in wavelength of the first light source at the time thatthe temperature change ΔT takes place.
 59. The optical pickup apparatusof claim 1, wherein the converging optical system comprises an objectivelens and the following formula is satisfied: 0.2×10⁻⁶ /°C.<ΔWSA3·λ1/{f·(NA1)⁴ ΔT}<2.2×10⁻⁶ /° C. where NA1 is the numericalaperture of the first optical information recoding medium for the firstlight flux at an image side of the objective lens, λ1 is the wavelengthof the first light flux, ΔT is an ambient temperature change; and ΔWSA3is a changed amount of a third order spherical aberration component of awave-front aberration of a light flux converged onto an opticalinformation recording plane in the case of reproducing information fromor recording information on the optical information recording medium byusing the first light flux.
 60. The optical pickup apparatus of claim 1,wherein the converging optical system comprises an objective lens,wherein in case that the first light flux is used, the first light fluxpositioned inside a predetermined numerical aperture of a first opticalinformation recording medium at an image side of the objective lens isconverged onto a first information recording plane of a first opticalinformation recording medium on a condition that a wave-front aberrationis not larger than 0.07 λrms, wherein a wave-front aberration of thefirst light flux passing outside the predetermined numerical aperture islarger than 0.07 λrms on the first information recording plane, andwherein in case that the second light flux is used, the second lightflux passing inside the predetermined numerical aperture and the secondlight flux passing outside the predetermined numerical aperture areconverged on a second information recording plane of a second opticalinformation recording medium on a condition that a wave-front aberrationis not larger than 0.07 λrms, or wherein in case that the second lightflux is used, the second light flux positioned inside a predeterminednumerical aperture of a second optical information recording medium atan image side of the objective lens is converged onto a firstinformation recording plane of a second optical information recordingmedium on a condition that a wave-front aberration is not larger than0.07 λrms, wherein a wave-front aberration of the second light fluxpassing outside the predetermined numerical aperture is larger than 0.07λrms on the second information recording plane, and wherein in case thatthe first light flux is used, the first light flux passing inside thepredetermined numerical aperture and the first light flux passingoutside the predetermined numerical aperture are converged on a firstinformation recording plane on a condition that a wave-front aberrationis not larger than 0.07 λrms.
 61. The optical pickup apparatus of claim1, wherein the converging optical system comprises an objective lens,wherein in case that the first light flux is used, the first light fluxpositioned inside a predetermined numerical aperture of the firstoptical information recording medium at an image side of the objectivelens is converged onto a first information recording plane of a firstoptical information recording medium on a condition that a wave-frontaberration is not larger than 0.07 λrms, wherein the first light fluxpassing outside the predetermined numerical aperture is converged ontothe first information recording plane on a condition that a wave-frontaberration is not larger than 0.07 λrms or shaded so as not to reach tothe first information recording plane, and wherein in case that thesecond light flux is used, the second light flux passing inside thepredetermined numerical aperture and the second light flux passingoutside the predetermined numerical aperture are converged onto a secondinformation recording plane of a second optical information recordingmedium on a condition that a wave-front aberration is not larger than0.07 λrms, or wherein in case that the second light flux is used, thesecond light flux positioned inside a predetermined numerical apertureof the second optical information recording medium at an image side ofthe objective lens is converged onto a second information recordingplane of a second optical information recording medium on a conditionthat a wave-front aberration is not larger than 0.07 λrms, wherein, thesecond light flux passing outside the predetermined numerical apertureis converged onto the second information recording plane on a conditionthat a wave-front aberration is not larger than 0.07 λrms or shaded soas not to reach to the second information recording plane, and whereinin case that the first light flux is used, the first light flux passinginside the predetermined numerical aperture and the first light fluxpassing outside the predetermined numerical aperture are converged ontoa first information recording plane of a first optical informationrecording medium on a condition that a wave-front aberration is notlarger than 0.07 λrms.
 62. The optical pickup apparatus of claim 1,wherein the converging optical system comprises a objective lens, andwherein the first light flux of non-parallel light flux is allowed to gointo the objective lens when the first light flux is used, and thesecond light flux of non-parallel light flux is allowed to go into theobjective lens when the second light flux is used.
 63. The opticalpickup apparatus of claim 62, wherein the non-parallel light flux isdivergent light.
 64. The optical pickup apparatus of claim 62, whereinthe non-parallel light flux is convergent light.
 65. The optical pickupapparatus of claim 1, wherein the converging optical system comprises aobjective lens, and wherein the first light flux of parallel light fluxis allowed to go into the objective lens when the first light flux isused and the second light flux of non-parallel light flux is allowed togo into the objective lens when the second light flux is used, or thefirst light flux of non-parallel light flux is allowed to go into theobjective lens when the first light flux is used and the second lightflux of parallel light flux is allowed to go into the objective lenswhen the second light flux is used.
 66. The optical pickup apparatus ofclaim 65, wherein the non-parallel light flux is divergent light. 67.The optical pickup apparatus of claim 65, wherein the non-parallel lightflux is convergent light.
 68. The optical pickup apparatus of claim 1,wherein, and wherein the first light flux of parallel light flux isallowed to go into the objective lens when the first light flux is usedand the second light flux of parallel light flux is allowed to go intothe objective lens when the second light flux is used.
 69. The opticalpickup apparatus of claim 1, wherein the converging optical systemcomprises an objective lens and divergent degree changing means forchanging a degree of divergent of light flux coming into the objectivelens.
 70. The optical pickup apparatus of claim 1, wherein the photodetector is common to the first light flux and the second light flux.71. The optical pickup apparatus of claim 1, further comprising a secondphoto detector, wherein the photo detector is used for the first lightflux and the second photo detector is used for the second light flux.72. The optical pickup apparatus of claim 1, wherein the photo detectorand one of the first light source and the second light source are madein a unit.
 73. The optical pickup apparatus of claim 1, wherein thephoto detector, the first light source and the second light source aremade in a unit.
 74. The optical pickup apparatus of claim 1, furthercomprising a second photo detector, wherein the photo detector is usedfor the first light flux, the second photo detector is used for thesecond light flux, and the photo detector, the second image sensor, thefirst light source and the second light source are made in a unit. 75.The optical pickup apparatus of claim 1, wherein the first light sourceand the second light source are made in a unit.
 76. The optical pickupapparatus of claim 1, wherein over shoot is 0% to 20%.
 77. An opticalelement for use in an optical pickup apparatus for reproducinginformation from an optical information recording medium or for recodinginformation onto an optical information recording medium, comprising: anoptical axis, and a diffractive portion, wherein in case that the firstlight flux passes through the diffractive portion to generate at leastone diffracted ray, an amount of n-th ordered diffracted ray of thefirst light flux is greater than that of any other ordered diffractedray of the first light flux, and in case that the second light fluxwhose wavelength is different from that of the first light flux passesthrough the diffractive portion to generate at least one diffracted ray,an amount of n-th ordered diffracted ray of the second light flux isgreater than that of any other ordered diffracted ray of the secondlight flux, wherein a difference in wavelength between the first lightflux and the second light flux is 80 nm to 400 nm and n stands for aninteger other than zero.
 78. The optical element of claim 77, whereinthe optical pickup apparatus comprises a first light source for emittingfirst light flux having a first wavelength, a second light source foremitting second light flux having second wavelength, and an imagesensor.
 79. The optical element of claim 77, wherein the optical pickupapparatus reproduces information from at least two kinds of opticalinformation recording media or records information onto one of thedifferent kinds of optical information recording media, and wherein thefirst light source emits the first light flux for reproducinginformation from a first optical information recording medium or forrecording information onto a first optical information recording medium;and the second light source emits the second light flux for reproducinginformation from a second optical information recording medium or forrecording information onto a second optical information recordingmedium.
 80. The optical element of claim 79, wherein the optical elementis capable of converging the n-th ordered diffracted ray of the firstlight flux, which is generated at the diffractive portion by the firstlight flux being reached the diffractive portion, on a first informationrecording plane of the first optical information recording mediumthrough a first transparent substrate so as to reproduce informationrecorded on the first optical information recording medium or to recordinformation onto the first optical information recording medium, andwherein the optical element is capable of converging the n-th ordereddiffracted ray of the second light flux, which is generated at thediffractive portion by the second light flux being reached thediffractive portion on a second information recording plane of thesecond optical information recording medium through a second transparentsubstrate so as to reproduce information recorded in the second opticalinformation to record medium or recording information onto the secondoptical information recording medium.
 81. The optical element of claim80, wherein the optical pickup apparatus comprises an objective lens,wherein the converging optical system is capable of converging the n-thordered diffracted ray of the first light flux on the first informationrecording plane of the first optical information recording medium on acondition that a wave-front aberration is not larger than 0.07 λrms whena numerical aperture at an image side of the objective is within apredetermined numerical aperture of the first optical informationrecording medium, and wherein the converging optical system is capableof converging the n-th ordered diffracted ray of the second light fluxon a second information recording plane of the second opticalinformation recording medium on a condition that a wave-front aberrationis not larger than 0.07 λrms when a numerical aperture at the image sideof the objective is within a predetermined numerical aperture of thesecond optical information recordng medium.
 82. The optical element ofclaim 79, wherein the first optical information recording medium has afirst transparent substrate of thickness t1, and wherein the secondoptical information recording medium has a second transparent substrateof thickness t2, wherein the thickness t2 is different from thethickness t1.
 83. The optical element of claim 82, wherein the opticalpickup apparatus comprises an objective lens, wherein the convergingoptical system is capable of converging the n-th ordered diffracted rayof the first light flux on the first information recording plane of thefirst optical information recording medium on a condition that awave-front aberration is not larger than 0.07 λrms when a numericalaperture at the image side of the objective is within a predeterminednumerical aperture of the first optical information recording medium,and wherein the converging optical system is capable of converging then-th ordered diffracted ray of the second light flux onto a secondinformation recording plane of the second optical information recordingmedium on a condition that a wave-front aberration is not larger than0.07 λrms when a numerical aperture at the image side of the objectiveis within a predetermined numerical aperture of the second opticalrecording medium.
 84. The optical element of claim 82, wherein thefollowing formula is satisfied: λ1<λ2 and t1<t2 where λ1 is the wavelength of the first light flux, λ2 is the wave length of the secondlight flux, t1 is the thickness of the first transparent substrate, andt2 is the thickness of the second transparent substrate.
 85. The opticalelement of claim 84, wherein the following formula is satisfied: NA1>NA2Where NA1 is a predetermined numerical aperture of the first opticalinformation recording medium for the first light flux at an image sideof the objective lens, and NA2 is a predetermined numerical aperture thesecond optical information recording medium for the second light flux atan image side of the objective lens.
 86. The optical element of claim85, wherein the n-th ordered diffracted ray is a positive first ordereddiffracted ray.
 87. The optical element of claim 85, wherein thefollowing formula is satisfied: 0.55 mm<t1<0.65 mm 1.1 mm<t2<1.3 mm 630nm<λ1<670 nm 760 nm<λ2<820 nm 0.55<NA1<0.68 0.40<NA2<0.55
 88. Theoptical element of claim 87, wherein the optical element is an objectivelens, λ1=650 nm, t1=0.6 mm, and NA1=0.6 and wherein in case that thefirst light flux which is composed of parallel rays and have a uniformintensity distribution are introduced in the objective lens and areconverged on the first information recording plane through the firsttransparent substrate, a diameter of converged spot is 0.88 μm to 0.91μm at the best focusing condition.
 89. The optical element of claim 87,wherein the optical element is an objective lens, λ1=650 nm, t1=0.6 mm,and NA=0.65 and wherein in case that the first light flux which iscomposed of parallel rays and have a uniform intensity distribution areintroduced in the objective lens and are converged on the firstinformation recording plane through the first transparent substrate, adiameter of converged spot is 0.81 μm to 0.84 μm at the best focusingcondition.
 90. The optical element of claim 87, wherein t1 is 0.6 mm, t2is 1.2 mm, λ1 is 650 nm, λ2 is 780 nm, NA1 is 0.6 and NA2 is 0.45. 91.The optical element of claim 85, wherein the optical element is anobjective lens, and in case that the objective lens converges the n-thordered diffracted ray of the second light flux on the secondinformation recording plane of the second optical information recordingmedium, the spherical aberration comprises a discontinuing section in atleast one place.
 92. The optical element of claim 91, wherein thespherical aberration comprises the discontinuing section at a place nearNA2.
 93. The optical element of claim 91, wherein the sphericalaberration comprises the discontinuing section at a place at which NA is0.45.
 94. The optical element of claim 91, wherein the sphericalaberration comprises the discontinuing section at a place at which NA is0.5.
 95. The optical element of claim 91, wherein the objective lensconverges the n-th ordered diffracted ray having a numerical aperturesmaller than NA1 in the first light flux having passed over thediffractive portion on the first information recording plane of thefirst recording medium such that the wave-front aberration at the bestimage point is 0.07 λrms and the objective lens converges the n-thordered diffracted ray having a numerical aperture smaller than that ofthe discontinuing section in the second light flux having passed overthe diffractive portion on the second information recording plane of thesecond recording medium such that the wave-front aberration at the bestimage point is 0.07 λrms.
 96. The optical element of claim 85, whereinthe optical element is an objective lens, and in case that theconverging optical system converges the n-th ordered diffracted ray inthe second light flux having passed over the diffractive portion on thesecond information recording plane of the second optical informationrecording medium in order to conduct the recording or the reproducingfor the second optical information recording medium, the sphericalaberration is continued without having a discontinuing section.
 97. Theoptical element of claim 96, wherein the spherical aberration at NA1 isnot smaller than 20 μm and the spherical aberration at NA2 is not largerthan 10 μm.
 98. The optical element of claim 82, wherein the followingformula is satisfied: λ1<λ2 and t1>t2 where λ1 is the wave length of thefirst light flux, λ2 is the wave length of the second light flux, t1 isthe thickness of the first transparent substrate, and t2 is thethickness of the second transparent substrate.
 99. The optical elementof claim 98, wherein the n-th ordered diffracted ray is a negative firstordered diffracted ray.
 100. The optical element of claim 77, wherein adiffracting efficiency at the diffractive portion for the n-th ordereddiffracted ray of the first light flux is A% and a diffractingefficiency for another ordered diffracted ray of the first light flux isB%, the diffracting efficiencies satisfy the following formula: A−B≧10,and a diffracting efficiency at the diffractive portion for the n-thordered diffracted ray of the second light flux is A′% and a diffractingefficiency for another ordered diffracted ray of the second light fluxis B′%, the diffracting efficiencies satisfy the following formula:A′−B′≧10.
 101. The optical element of claim 100, wherein a diffractingefficiency at the diffractive portion for the n-th ordered diffractedray of the first light flux is A% and a diffracting efficiency foranother ordered diffracted ray of the first light flux is B%, thediffracting efficiencies satisfy the following formula: A−B≧50, and adiffracting efficiency at the diffractive portion for the n-th ordereddiffracted ray of the second light flux is A′% and a diffractingefficiency for another ordered diffracted ray of the second light fluxis B′%, the diffracting efficiencies satisfy the following formula:A′−B′≧50.
 102. The optical element of claim 77, wherein the diffractiveportion comprises a plurality of annular bands formed coaxially aroundthe optical axis or around a point near the optical axis as a center.103. The optical element of claim 102, wherein a phase differencefunction expressed by power series indicating each position of theplurality of annular bands has a coefficient except zero in at least oneterm except 2nd power term.
 104. The optical element of claim 102,wherein a phase difference function expressed by power series indicatingeach position of the plurality of annular bands has a coefficient exceptzero in 2nd power term.
 105. The optical element of claim 102, wherein aphase difference function expressed by power series indicating eachposition of the plurality of annular bands has not 2nd power term. 106.The optical element of claim 102, wherein a sign of negative or positiveof a diffracting effect added by the diffractive portion is switched atleast one time in a direction departing from the optical axisperpendicularly to the optical axis.
 107. The optical element of claim106, wherein the plurality of annular bands in the diffractive portionare blazed, a stepped section in an annular band located at a side closeto the optical axis is located at a side distant from the optical axis,and a stepped section in an annular band located at a side distant fromthe optical axis is located at a side close to the optical axis. 108.The optical element of claim 106, wherein the plurality of annular bandsin the diffractive portion are blazed, a stepped section in an annularband located at a side close to the optical axis is located at a sideclose to the optical axis, and a stepped section in an annular bandlocated at a side distant from the optical axis is located at a sidedistant from the optical axis.
 109. The optical element of claim 102,wherein the pickup apparatus comprises an objective lens, a pitch Pf ofthe annular bands in the diffractive portion corresponding to a maximumnumerical aperture at the image side of the objective lens and a pitchPh of the annular bands in the diffractive portion corresponding to halfof the maximum numerical aperture satisfy the following formula.0.4≦|(Ph/Pf)−2|≦25
 110. The optical element of claim 102, wherein thediffractive portion comprises a first diffractive pattern and a seconddiffractive pattern and the second diffractive pattern is locateddistant from the optical axis more than the first diffractive pattern.111. The optical element of claim 110, wherein the amount of n-thordered diffracted ray is generated more than that of other ordereddiffracted ray in the first light flux having passed over the firstdiffractive pattern of the diffractive portion, the amount of the n-thordered diffracted ray is generated more than that of other ordereddiffracted ray in the second light flux having passed over the firstdiffractive pattern of the diffractive portion, an amount of the n-thordered diffracted ray is generated more than that of other ordereddiffracted ray in the first light flux having passed over the seconddiffractive pattern of the diffractive portion, and an amount of 0-thordered diffracted ray is generated more than that of other ordereddiffracted ray in the second light flux having passed over the seconddiffractive pattern of the diffractive portion.
 112. The optical elementof claim 110, wherein an amount of n-th ordered diffracted ray isgenerated more than that of other ordered diffracted ray in the firstlight flux having passed over the first diffractive pattern of thediffractive portion, an amount of the n-th ordered diffracted ray isgenerated more than that of other ordered diffracted ray in the secondlight flux having passed over the first diffractive pattern of thediffractive portion, an amount of the 0-th ordered diffracted ray isgenerated more than that of other ordered diffracted ray in the firstlight flux having passed over the second diffractive pattern of thediffractive portion, and an amount of negative ordered diffracted rayexcept the n-th order is generated more than that of other ordereddiffracted ray in the second light flux having passed over the seconddiffractive pattern of the diffractive portion.
 113. The optical elementof claim 102, wherein the diffractive portion is provided on thesubstantially entire surface of a light flux-incoming surface or a lightflux-outgoing surface of the optical element.
 114. The optical elementof claim 102, wherein an area of the diffractive portion is 10% to 90%of an area of a light flux-incoming surface or a light flux-outgoingsurface of the optical element.
 115. The optical element of claim 102,wherein a number of steps on the annular bands in the diffractiveportion is 2 to
 45. 116. The optical element of claim 115, wherein anumber of steps on the annular bands in the diffractive portion is 2 to15.
 117. The optical element of claim 102, wherein a depth, in theoptical axial direction, of a stepped section on the annular bands inthe diffractive portion is not larger than 2 μm.
 118. The opticalelement of claim 102, wherein the pitch of the diffractive portion at apoint at which NA=0.4 is 10 μm to 70 μm.
 119. The optical element ofclaim 77, wherein the optical element is a lens having a refractingsurface.
 120. The optical element of claim 119, wherein the opticalelement is an objective lens.
 121. The optical element of claim 119,wherein the optical element is a collimator lens.
 122. The opticalelement of claim 77, wherein the optical element is not an objectivelens and a collimator lens.
 123. The optical element of claim 120,wherein the objective lens comprises a flange section on a outercircumference thereof.
 124. The optical element of claim 120, whereinthe refracting surface of the objective lens is an aspherical surface.125. The optical element of claim 119, wherein the lens is made of amaterial whose Abbe number νd is not smaller than
 50. 126. The opticalelement of claim 119, wherein the lens is a plastic lens.
 127. Theoptical element of claim 119, wherein the lens is a glass lens.
 128. Theoptical element of claim 77, wherein the n-th ordered diffracted ray isa positive first ordered diffracted ray or a negative first ordereddiffracted ray.
 129. The optical element of claim 77, wherein adiffracting efficiency of the n-th ordered diffracted ray by thediffractive portion becomes maximum in a wavelength between thewavelength of the first light flux and the wavelength of the secondlight flux.
 130. The optical element of claim 77, wherein a diffractingefficiency of the n-th ordered diffracted ray by the diffractive portionbecomes maximum in the wavelength of the first light flux or in thewavelength of the second light flux.
 131. The optical element of claim77, wherein the optical element satisfies the following formula:−0.0002/° C.<Δn/ΔT<− 0.00005° C. wherein ΔT is a temperature change, andΔn is a change in refractive index of the lens.
 132. The optical elementof claim 77, wherein the optical pickup apparatus comprises an objectivelens, wherein in case that the first light flux is used, the first lightflux positioned inside a predetermined numerical aperture of a firstoptical information recording medium at the image side of the objectivelens is converged onto a first information recording plane of a firstoptical information recording medium on a condition that a wave-frontaberration is not larger than 0.07 λrms, wherein a wave-front aberrationof the first light flux passing outside the predetermined numericalaperture is larger than 0.07 λrms on the first information recordingplane, and wherein in case that the second light flux is used, thesecond light flux passing inside the predetermined numerical apertureand the second light flux passing outside the predetermined numericalaperture are converged on a second information recording plane of asecond optical information recording medium on a condition that awave-front aberration is not larger than 0.07 λrms, or wherein in casethat the second light flux is used, the second light flux positionedinside a predetermined numerical aperture of a second opticalinformation recording medium at the image side of the objective lens isconverged onto a first information recording plane of a second opticalinformation recording medium on a condition that a wave-front aberrationis not larger than 0.07 λrms, wherein a wave-front aberration of thesecond light flux passing outside the predetermined numerical apertureis larger than 0.07 λrms on the second information recording plane, andwherein in case that the first light flux is used, the first light fluxpassing inside the predetermined numerical aperture and the first lightflux passing outside the predetermined numerical aperture are convergedon a first information recording plane on a condition that a wave-frontaberration is not larger than 0.07 λrms.
 133. The optical element ofclaim 77, wherein the optical pickup apparatus comprises an objectivelens, wherein in case that the first light flux is used, the first lightflux positioned inside a predetermined numerical aperture at the imageside of the objective lens is converged onto a first informationrecording plane of a first optical information recording medium on acondition that a wave-front aberration is not larger than 0.07 λrms,wherein the first light flux passing outside the predetermined numericalaperture is converged onto the first information recording plane on acondition that a wave-front aberration is not larger than 0.07 λrms orshaded so as not to reach to the first information recording plane, andwherein in case that the second light flux is used, the second lightflux passing inside the predetermined numerical aperture and the secondlight flux passing outside the predetermined numerical aperture areconverged onto the second information recording plane of the secondoptical information recording medium on a condition that a wave-frontaberration is not larger than 0.07 λrms, or wherein in case that thesecond light flux is used, the second light flux positioned inside apredetermined numerical aperture of the second optical informationrecording medium at the image side of the objective lens is convergedonto the second information recording plane of the second opticalinformation recording medium on a condition that a wave-front aberrationis not larger than 0.07 λrms, wherein the second light flux passingoutside the predetermined numerical aperture is converged onto thesecond information recording plane on a condition that a wave-frontaberration is not larger than 0.07 λrms or shaded so as not to reach tothe second information recording plane, and wherein in case that thefirst light flux is used, the first light flux passing inside thepredetermined numerical aperture and the first light flux passingoutside the predetermined numerical aperture are converged onto thefirst information recording plane of the first optical informationrecording medium on a condition that a wave-front aberration is notlarger than 0.07 λrms.
 134. The optical pickup apparatus of claim 77,wherein over shoot is 0% to 20%.
 135. An apparatus for reproducinginformation from an optical information recording medium or forrecording information onto the optical information recording mediumcomprising; an optical pickup apparatus, comprising a first light sourcefor emitting first light flux having a first wavelength; a second lightsource for emitting second light flux having a second wavelength, thefirst wavelength being different from the second wavelength; aconverging optical system having an optical axis, a diffractive portion,and a photo detector, wherein in case that the first light flux passesthrough the diffractive portion to generate at least one diffracted ray,an amount of n-th ordered diffracted ray of the first light flux isgreater than that of any other ordered diffracted ray of the first lightflux, and in case that the second light flux passes through thediffractive portion to generate at least one diffracted ray, an amountof n-th ordered diffracted ray of the second light flux is greater thanthat of any other ordered diffracted ray of the second light flux, wheren stands for an integer other than zero.
 136. A method of reproducinginformation from or recording information on at least two kinds ofoptical information recording media by an optical pickup apparatuscomprising a first light source, a second light source, a photo detectorand a converging optical system having an optical axis and a diffractiveportion, the method comprising steps of; emitting first light flux fromthe first light source or second light flux from the second light flux,wherein a wavelength of the second light flux is different from awavelength of the first light flux; letting the first light or thesecond light flux pass through the diffractive portion to generate atleast one diffracted ray of the first light flux or a least onediffracted ray of the second light flux, wherein when an amount of n-thordered diffracted ray among the at least one diffracted ray of thefirst light flux is greater than an amount of any other ordereddiffracted ray of the first light flux, an amount of n-th ordereddiffracted ray among the at least one diffracted ray of the second lightflux is greater than an amount of any other ordered diffracted ray ofthe second light flux, converging, by the converging optical system, then-th ordered diffracted ray of the first light flux onto a firstinformation recording plane of a first optical information recordingmedium or the n-th ordered diffracted ray of the second light flux ontoa second information recording plane of a second optical informationrecording medium in order for the optical pickup apparatus to record theinformation onto or reproduce the information from the first informationrecording plane or the second information recording plane, detecting, bya photo detector, a first reflected light flux of the converged n-thordered diffracted light from the first information recording plane or asecond reflected light flux of the converged n-th ordered diffractedlight from the second information recording plane; where n stands for aninteger other than zero.